Lake Sturgeon Waters and Fisheries in New York State

Historic and contemporary records of lake sturgeon (Acipenser fulvescens) occurrences in new York State have been assembled in this report to assist in planning and prioritizing the areas for restoration. This has become important because information about this threatened species is not easily assembled nor easily retrieved from the few remaining fishermen. Lake sturgeon were identified in 17 waters of New York State in the Great Lakes drainage including Lakes Erie, Ontario, Champlain, and the Niagara and St. Lawrence rivers. Two other rivers in the Laurentain Great Lakes drainage had self-sustaining populations, five others historically supported spawning runs, and five other waters had historical records of use or relict populations. Lake Erie provided the largest historic fishery for lake sturgeon in New York State (1,678 tonne reported in 1885) followed by Lake Ontario (292 tonne reported in 1890). All the major waters (the first five identified above) had large harvests, and two tributaries to the St. Lawrence River, the Grasse and Oswegatchie rivers, also provided commercial harvests. The Great Lakes fisheries were reduced to abandonment by the 1940s and the remaining ones were discontinued by the 1960s. Currently, lake sturgeon are self-sustaining at very low levels in the upper Niagara, St. Lawrence, and the Grasse rivers. The fish is protected from harvest in all areas but one.     

Long-term Trends in the Seasonal Cycle of Great Lakes Water Levels

Numerous long-term trends in the rate-of-change in monthly mean Great Lakes water levels are identified for the period 1860 to 1998. Statistically significant trends are found for 2, 4, 5, and 7 months of the year for Lakes Superior, Michigan-Huron, Erie, and Ontario, respectively. Many of the trends translate into large changes in net water flux (600 to 1,700 m³/s). In each case, significant positive trends are roughly offset by negative trends during other times of the year. Together with similar trends in monthly lake level anomalies (deviations from the annual mean), these trends indicate important changes in the seasonal cycle of Great Lakes water levels. Specifically, Lakes Erie and Ontario are rising and falling (on an annual basis) roughly one month earlier than they did 139 years ago. Maximum lake levels for Lake Superior are also slightly earlier in the year, and the amplitude of the seasonal cycle of Lake Ontario is found to increase by 23% over the 139-year period. Some of the changes are consistent with the predicted impacts of global warming on spring snowmelt and runoff in the Great Lakes region. Other potential contributors to the observed trends include seasonal changes in precipitation and humaninduced effects such as lake regulation and changes in land use.     

Concentrations and loads of nutrients and major ions in the Niagara River, 1975–2018

Environment and Climate Change Canada has monitored Niagara River water quality in support of the Great Lakes Water Quality Agreement since establishing a fixed site at Niagara-on-the-Lake in 1975. Using over 40 years of data from this site along with the Fort Erie location added in 1983, we examine the status and trends of concentrations and loadings of nutrients and major ions and assess evidence of sources between the two stations. Trends were observed for the majority of measured parameters and there is strong agreement between trends in concentrations and loadings which are generally higher at the downstream site; however, upstream/downstream differences indicate relatively little loading occurs along the length of the river itself. For total phosphorus (TP), inputs from Lake Erie via the Niagara River account for the majority of loading to Lake Ontario and, in some years, exceed the 7000 MTA Lake Ontario target. Between 2014 and 2018, we calculate the mean Niagara River TP loading to be 5275 MTA. We highlight the major changes in water quality constituents over time, including TP, and reveal increased seasonal consumption of TP and SiO₂, reflecting potential increases in the biological productivity in Lake Erie. The long and rich Niagara River dataset, which comprises year round sampling (including rare winter data), provides detailed tracking of changing Great Lakes water quality and could be further utilized to assess the impacts of climate change, improve understanding of diatom and harmful algal bloom dynamics, and enhance knowledge of in-lake major ion and nutrient dynamics.     

Laurentian Great Lakes Hydrology and Lake Levels under the Transposed 1993 Mississippi River Flood Climate

The Laurentian Great Lakes are North America's largest water resource, and include six large water bodies (Lakes Superior, Michigan, Huron, Erie, Ontario, and Georgian Bay), Lake St. Clair, and their connecting channels. Because of the relatively small historical variability in system lake levels, there is a need for realistic climate scenarios to develop and test sensitivity and resilience of the system to extreme high lake levels. This is particularly important during the present high lake level regime that has been in place since the late 1960s. In this analysis, we use the unique climate conditions which resulted in the 1993 Mississippi River flooding as an analog to test the sensitivity of Great Lakes hydrology and water levels to a rare but actual climate event. The climate over the Upper Mississippi River basin was computationally shifted, corresponding to a conceptual shift of the Great Lakes basin 10̊ west and 2̊ south. We applied a system of hydrological models to the daily meteorological time series and determined daily runoff, lake evaporation, and net basin water supplies. The accumulated net basin supplies from May through October 1993 for the 1993 Mississippi River flooding scenario ranged from a 1% decrease for Lake Superior to a large increase for Lake Erie. Water levels for each lake were determined from a hydro-logic routing model of the system. Lakes Michigan, Huron, and Erie were most affected. The simulated rise in Lakes Michigan and Huron water levels far exceeded the historically recorded rise with both lakes either approaching or setting record high levels. This scenario demonstrates that an independent anomalous event, beginning with normal lake levels, could result in record high water levels within a 6- to 9-month period. This has not been demonstrated in the historical record or by other simulation studies.     

Temporal Effects of St. Clair River Dredging on Lakes St. Clair and Erie Water Levels and Connecting Channel Flow

A Great Lakes hydrologic response model was used to study the temporal effects of St. Clair River dredging on Lakes St. Clair and Erie water levels and connecting channel flows. The dredging has had a significant effect on Great Lakes water levels since the mid-1980s. Uncompensated dredging permanently lowers the water levels of Lakes Michigan and Huron and causes a transitory rise in the water levels of Lakes St. Clair and Erie. Two hypothetical dredging projects, each equivalent to a 10 cm lowering of Lakes Michigan and Huron, were investigated. This lowering is approximately half the effect of the 7.6 and 8.2 meter dredging projects. In the first case the dredging was assumed to occur over a single year while in the second it was spread over a 2-year period. The dredging resulted in a maximum rise of 6 cm in the downstream levels of Lakes St. Clair and Erie. The corresponding increase in connecting channel flows was about 150 m³s^?1. The effects were found to decrease over a 10-year period with a half-life of approximately 3 years. The maximum effects on Lake Erie lagged Lake St. Clair by about 1 year.     

An adaptive management approach for implementing multi-jurisdictional response to grass carp in Lake Erie

The Great Lakes are influenced by established aquatic invasive species (AIS) and the threat of new invaders persists. Grass carp, one of four species commonly referred to as Asian carp, are considered invasive because of their ability to adversely modify aquatic habitat through consumption of aquatic macrophytes. Grass carp have been infrequently detected in the Great Lakes since the mid-1980s. More frequent reports of grass carp captures from commercial fishermen in the early 2010’s elevated the concern of the potential risk of colonization in Lake Erie. This paper provides a case study detailing the development and implementation of a multi-jurisdictional response strategy for grass carp in Lake Erie. To respond to threats of grass carp in Lake Erie, Michigan and Ohio Departments of Natural Resources led targeted responses using a collaborative multi-jurisdictional approach, while simultaneously investing in reducing critical life-history uncertainties to refine strategies in an adaptive and science-based manner. Efforts to address uncertainties about grass carp life history documented spawning in two Lake Erie tributaries. Building on these early responses, the binational Lake Erie Committee developed a five-year adaptive response framework to guide response actions. The collaborative response efforts resulted in the capture and removal of 184 fertile grass carp since 2014, and efforts are ongoing to increase effectiveness of strategies to achieve desired population reduction. Coordinated grass carp response actions under the five-year strategy will continue using adaptive management principles with outcomes providing useful insights for adapting existing response frameworks and more broadly for AIS responses implemented elsewhere.     

Tributary use and large-scale movements of grass carp in Lake Erie

Infrequent captures of invasive, non-native grass carp (Ctenopharyngodon idella) have occurred in Lake Erie over the last 30+ years, with recent evidence suggesting wild reproduction in the lake’s western basin (WB) is occurring. Information on grass carp movements in the Laurentian Great Lakes is lacking, but an improved understanding of large-scale movements and potential areas of aggregation will help inform control strategies and risk assessment if grass carp spread to other parts of Lake Erie and other Great Lakes. Twenty-three grass carp captured in Lake Erie’s WB were implanted with acoustic transmitters and released. Movements were monitored with acoustic receivers deployed throughout Lake Erie and elsewhere in the Great Lakes. Grass carp dispersed up to 236 km, with approximately 25% of fish dispersing greater than 100 km from their release location. Mean daily movements ranged from <0.01 to 2.49 km/day, with the highest daily averages occurring in the spring and summer. The Sandusky, Detroit, and Maumee Rivers, and Plum Creek were the most heavily used WB tributaries. Seventeen percent of grass carp moved into Lake Erie’s central or eastern basins, although all fish eventually returned to the WB. One fish emigrated from Lake Erie through the Huron-Erie Corridor and into Lake Huron. Based on our results, past assessments may have underestimated the potential for grass carp to spread in the Great Lakes. We recommend focusing grass carp control efforts on Sandusky River and Plum Creek given their high use by tagged fish, and secondarily on Maumee and Detroit Rivers.     

The Sea Lamprey in Lake Erie: a Case History

Sea lampreys (Petromyzon marinus), first reported in Lake Erie in 1921, emigrated from Lake Ontario via the Welland Canal. It was not until the advent of pollution abatement, stream rehabilitation, and salmonid enhancement programs that sea lampreys proliferated. The Great Lakes Fishery Commission (GLFC), in co-operation with state, provincial, and federal fisheries agencies, implemented an integrated sea lamprey management (IMSL) plan for Lake Erie in 1986. Suppression of sea lampreys was nearly immediate, as indicated by declining larval-, parasitic-, and spawning-phase abundance, while survival of lake trout (Salvelinus namaycush) was markedly improved. Consistent with their vision statement, the GLFC began reducing lampricide use by the mid-1990s, while increasing reliance on alternative control methodologies. Reduction of treatment effort coincided with the development of new lampricide application techniques and treatment selection criteria, in addition to heightened regional concern for the impact of lampricide on non-target species. Subsequently, Lake Erie's sea lamprey numbers have rebounded, and marking rates on lake trout have approached pre-control levels. It is hypothesized that Lake Erie's rising abundance is primarily fuelled by untreated and residual larval populations, although some migration of parasitic-phase sea lampreys from Lake Huron is suspected. Model simulations infer that treatment effort on Lake Erie was sub-optimal from 1995 to 1998. Beginning in 1999, the GLFC enhanced measures to identify and control sources of sea lampreys. Based on historical abundance patterns and model results, it is anticipated that intensified management in Lake Erie will reduce sea lamprey numbers and provide an opportunity for lake trout restoration.     

A modeling study to determine the contribution of interbasin versus intrabasin phosphorus loads on the southwestern nearshore of Lake Ontario

Elevated phosphorus and nuisance algae such as Cladophora have been persistent environmental concerns in the coastal areas of Lake Ontario. Phosphorus is regarded as one of the drivers of nearshore Cladophora and the most likely mitigation that can be used to control levels of this nuisance algae in the lakes. The Niagara River, carrying the Lake Erie interbasin load, is the major contributor of the overall phosphorus load to Lake Ontario. Due to circulation patterns in the lake, this contribution is especially significant in the southwestern nearshore areas. Here we apply a mathematical model to provide insight into the relative contribution of the Niagara River versus loadings from local rivers (intrabasin loads) on the nearshore phosphorus concentrations in this region. We performed numerical experiments to determine to what extent the Niagara, Genesee and smaller local rivers impact the nearshore (<20 m depth) phosphorus concentrations. Our model results show that the Niagara River dominates the nearshore region between its discharge location and the Genesee River’s mouth, but the Genesee River strongly impacts the nearby Ontario Beach region in the very nearshore (<5 m depth). Smaller rivers have some impact close to their discharge locations. However, uncertainty with the Niagara River phosphorus load is the limiting factor in making any credible nearshore phosphorus predictions. Model accuracy is also impacted by insufficient short time scale phosphorus loads for all of the rivers, the dynamic nature of the lake circulation in shallow nearshore areas, and the simplified assumptions of the model.     

Associations between Breeding Marsh Bird Abundances and Great Lakes Hydrology

We used Great Lakes hydrologic data and bird monitoring data from the Great Lakes Marsh Monitoring Program from 1995–2002 to: 1) evaluate trends and patterns of annual change in May-July water levels for Lakes Ontario, Erie, and Huron-Michigan, 2) report on trends of relative abundance for birds breeding in Great Lakes coastal marshes, and 3) correlate basin-wide and lake-specific annual indices of bird abundance with Great Lakes water levels. From 1995–2002, average May, June, and July water levels in all lake basins showed some annual variation, but Lakes Erie and Huron-Michigan had identical annual fluctuation patterns and general water level declines. No trend was observed in Lake Ontario water levels over this period. Abundance for five of seven marsh birds in Lake Ontario wetlands showed no temporal trends, whereas abundance of black tern (Chlidonias niger) declined and that of swamp sparrow (Melospiza georgiana) increased from 1995–2002. In contrast, abundances of American coot (Fulica americana), black tern, common moorhen (Gallinula chloropus), least bittern (Ixobrychus exilis), marsh wren (Cistorthorus palustris), pied-billed grebe (Podilymbus podiceps), sora (Porzana carolina), swamp sparrow, and Virginia rail (Rallus limicola) declined within marshes at Lakes Erie and Huron/Michigan from 1995–2002. Annual abundances of several birds we examined showed positive correlations with annual lake level changes in non-regulated Lakes Erie and Huron/Michigan, whereas most birds we examined in Lake Ontario coastal wetlands were not correlated with suppressed water level changes of this lake. Overall, our results suggest that long-term changes and annual water level fluctuations are important abiotic factors affecting abundance of some marsh-dependent birds in Great Lakes coastal marshes. For this reason, wetland bird population monitoring initiatives should consider using methods in sampling protocols, or during data analyses, to account for temporal and spatial components of hydrologic variability that affect wetlands and their avifauna.     

Status of the major aquaculture carps of China in the Laurentian Great Lakes Basin

There is concern of economic and environmental damage occuring if any of the four major aquacultured carp species of China, black carp Mylopharyngodon piceus, bighead carp Hypophthalmichthys nobilis, silver carp H. molitrix, or grass carp Ctenopharyngodon idella, were to establish in the Laurentian Great Lakes. All four are reproducing in the Mississippi River Basin. We review the status of these fishes in relation to the Great Lakes and their proximity to pathways into the Great Lakes, based on captures and collections of eggs and larvae. No black carp have been captured in the Great Lakes Basin. One silver carp and one bighead carp were captured within the Chicago Area Waterway System, on the Great Lakes side of electric barriers designed to keep carp from entering the Great Lakes from the greater Mississippi River Basin. Three bighead carp were captured in Lake Erie, none later than the year 2000. By December 2019, at least 650 grass carps had been captured in the Great Lakes Basin, most in western Lake Erie, but none in Lake Superior. Grass carp reproduction has been documented in the Sandusky and Maumee rivers in Ohio, tributaries of Lake Erie. We also discuss environmental DNA (eDNA) results as an early detection and monitoring tool for bighead and silver carps. Detection of eDNA does not necessarily indicate presence of live fish, but bigheaded carp eDNA has been detected on the Great Lakes side of the barriers and in a small proportion of samples from the western basin of Lake Erie.     

Genome-wide genetic diversity may help identify fine-scale genetic structure among lake whitefish spawning groups in Lake Erie

In Lake Erie, lake whitefish Coregonus clupeaformis supported lucrative fisheries before populations were decimated by overfishing and water quality degradation. In recent years, there has been a renewed interest in lake whitefish and management of the fishery they support. Lake whitefish spawn on several reefs throughout Lake Erie, but the relative recruitment dynamics and contributions of spawning groups to the fishery are not well understood. Modern high-throughput sequencing approaches offer new opportunities to census population diversity and to identify subtle differences among closely related populations. We used high-throughput sequencing data to evaluate the genetic structure and diversity of lake whitefish collected opportunistically across broad spatial scales in Lake Erie. Using RAD-capture (Rapture), we sequenced and genotyped individuals (N = 88) from the west, central, and east basin of Lake Erie at 120,268 single nucleotide polymorphisms (SNPs). Lake whitefish from Niagara and Crib Reefs (west basin) diverged from the three collections. Interestingly, these were the only lake whitefish collected during the act of spawning (late November), and all other fish were collected pre-spawn (August-early November). These results suggest that some lake whitefish spawning reefs may be reproductively isolated, though definition of these groups into stocks will require more intentional sampling during the act of spawning.     

Large-Scale Storm Damage on the U.S. Shores of the Great Lakes

Storm Data from the National Oceanic and Atmospheric Administration provides a data set for examining the spatial and temporal distribution of storm damage caused by large-scale, cyclonic storms on the U.S. shoreline of the Great Lakes for the period 1959–1990. On average, damage reports are much more frequent during high lake levels. Seasonally, the number reaches a maximum in November, declines during the winter months, and reaches a secondary maximum in April. This decrease in the winter months may be due to the protective ice cover on the lakes. Although Michigan received the most damage reports, Illinois, New York, and Ohio have a higher density of reports. Lake Erie and Lake Michigan are most frequently mentioned in the reports. A comparison of dollar losses shows that 1984 and 1985 were by far the costliest years since 1959. Comparison with a similar high-water period in the mid-1970s suggests that shorelines were much more vulnerable to storm damage in the mid-1980s when water levels were higher.     

Stability Effects on Great Lakes Evaporation

The effects of atmospheric stability on Great Lakes evaporation computed by the modified mass transfer method have been evaluated by analysis of stability effects on the variable mass transfer coefficient, land to lake data adjustments, and ice-cover reduction of evaporation during winter. The Great Lakes which produce extreme results, Lakes Superior and Erie, and a much smaller water body within the Great Lakes chain, Lake St. Clair, were studied. Comparison of these evaporation estimates with previous studies, which excluded variable stability effects, shows that the previous studies of Lake Superior produced generally similar total annual water loss from the lake, but significantly overestimated both the seasonal high evaporation and the condensation rates. These tended to balance each other. The atmospheric conditions over Lakes Erie and St. Clair do not become as strongly stable and they normally do not exhibit large condensation. Previous evaporation studies for these lakes indicate generally higher evaporation rates, with significant overestimation of the total annual water losses (25%).     

Historical changes and current status of crayfish diversity and distribution in the Laurentian Great Lakes

Despite increasing recognition of the importance of invertebrates, and specifically crayfish, to nearshore food webs in the Laurentian Great Lakes, past and present ecological studies in the Great Lakes have predominantly focused on fishes. Using data from many sources, we provide a summary of crayfish diversity and distribution throughout the Great Lakes from 1882 to 2008 for 1456 locations where crayfish have been surveyed. Sampling effort was greatest in Lake Michigan, followed by lakes Huron, Erie, Superior, and Ontario. A total of 13 crayfish species occur in the lakes, with Lake Erie having the greatest diversity (n = 11) and Lake Superior having the least (n = 5). Five crayfish species are non-native to one or more lakes. Because Orconectes rusticus was the most widely distributed non-native species and is associated with known negative impacts, we assessed its spread throughout the Great Lakes. Although O. rusticus has been found for over 100 years in Lake Erie, its spread there has been relatively slow compared to that in lakes Michigan and Huron, where it has spread most rapidly since the 1990s and 2000, respectively. O. rusticus has been found in both lakes Superior and Ontario for 22 and 37 years, respectively, and has expanded little in either lake. Our broad spatial and temporal assessment of crayfish diversity and distribution provides a baseline for future nearshore ecological studies, and for future management efforts to restore native crayfish and limit non-native introductions and their impact on food web interactions.     

Characterizing Seiche and Tide-driven Daily Water Level Fluctuations Affecting Coastal Ecosystems of the Great Lakes

Seiches in the Great Lakes probably play a role similar to that of tides in estuaries in organizing the structure and function of coastal wetlands and embayments, but information needed to test this idea is lacking. Past Great Lakes work has focused on enumerating frequencies of oscillation but without addressing their combined influence. Information on seiche magnitude is sparse and focused on extremes rather than typical levels, and tools that integrate magnitude and frequency components to derive net day-scale effects are lacking. This study uses water level time series to characterize daily fluctuation regimes for 51 stations around the Great Lakes. Distributions of fluctuation magnitude typically had long upper tails, with some level of activity always present. Logarithmic mean daily water level range varied from ∼4 cm in Lake Ontario to > 20 cm in Lake Erie, with largest values at the ends of lakes and in large bays. Oscillation frequency patterns were spatially variable and had both seiche and tide components. One-half the daily sum of water level increments is a computationally tractable metric of fluctuation intensity that integrates magnitude and frequency. This metric is directly interpretable as the column of water moved by all seiche and tide modes combined, which when multiplied by an area of interest yields the volume of water involved. Logarithmic mean values for this metric ranged from ∼10 cm in Lake Ontario to > 50 cm in Lake Erie. Data and tools provided will support future efforts to establish seiche and tide influences on Great Lakes wetlands and embayments.     

Great Lakes Flood Thresholds and Impacts

Using the location, data, and water levels from flood events along the Canadian shore of the Great Lakes, flood damage thresholds were determined to identify and compare water levels at which static and storm-induced high water impact shoreline interests on several shore reaches of Lakes Erie, Huron, Ontario, and St. Clair. Spatial differences identified may be related to several factors, including: 1) nearshore bathymetries; 2) extent of residential development along low-lying shorelines; 3) degree of riparian adjustment to flooding; and 4) location relative to dominant wind or storm directions. Correlation analyses found that flood damage levels are more closely correlated to fluctuations in static levels on Lakes Ontario, Huron, and St. Clair, while flood damage levels are more closely correlated to maximum instantaneous water levels on Lake Erie. Correlation analyses of individual gauge data identified locations possibly more susceptible to storm surges. A conservative approach to determining flood damage thresholds is suggested, being based on a standard deviation below the mean of maximum instantaneous flood levels for a given gauge. The standard deviation threshold, while lower than current “critical levels” used in management, is more representative of the majority of flood damage levels than thresholds based on lowest maximum instantaneous lake levels. However, caution is urged in applying any critical level solely based on water level gauge information as Great Lakes flooding is a highly site-specific phenomenon influenced by meteorologic factors.     

Application of a Depletion-Based Stock Reduction Analysis (DB-SRA) to lake sturgeon in Lake Erie

Lake Erie supported the greatest yield of lake sturgeon within the Laurentian Great Lakes near the end of the 19th century with >2000 metric tons caught at the peak of the fishery. The fishery collapsed by the 1920s when <1% of the previous peak catch was removed. Despite closures of the fishery, lake sturgeon remain rare in Lake Erie. We applied a depletion-based stock reduction analysis (DB-SRA) to the catch of lake sturgeon from 1879 to 1929 to gain estimates of sustainable fishery reference points and the historic carrying capacity of Lake Erie for lake sturgeon. We also simulated population growth of lake sturgeon from 1929 to the present with varying assumptions of the current carrying capacity of the lake. The estimated historic carrying capacity of lake sturgeon was 22,652 metric tons. During the height of the fishery, exploitation was as high as 37% which was more than an order of magnitude greater than that required for maximum sustainable yield. Projections of the population from 1929 to 2016 suggest sufficient time has passed since the collapse of the fishery that the population should have recovered to levels that would support a fishery at maximum sustainable yield. However, lake sturgeon remain rare in Lake Erie indicating that other factors such as habitat availability may be limiting their recovery. Our estimates of carrying capacity will be informative when setting recovery targets which consider the amount of habitat loss.     

Population Trends and Colony Locations of Double-crested Cormorants in the Canadian Great Lakes and Immediately Adjacent Areas, 1990–2000: A Manager's Guide

Numbers of nests of double-crested cormorants (Phalacrocorax auritus) were censused at up to 190 colonies in the early- mid- and late-1990s and 2000 on the Canadian Great Lakes and immediately adjacent U.S. waters. During those four periods, the number of nests increased from approximately 21,000 to 49,000 to 55,000 to 76,000. The total Great Lakes population of breeding cormorants for 2000 is estimated at 115,000 pairs (=nests). For the first time, all colony locations were plotted on lake-wide maps. Major nesting areas were eastern Lake Ontario, western Lake Erie, eastern Georgian Bay, all of the North Channel, and western Lake Superior. Average annual growth rates from the early 1990s to 2000 were much lower for most areas than during the 1980 to 1990 period. Three cormorant management issues are discussed: cormorant impacts on vegetation, on other colonial waterbirds, and on fisheries.     

Modeling Dissolved Oxygen in a Dredged Lake Erie Tributary

A two-dimensional numerical model was developed to study dissolved oxygen (DO) kinetics in a dredged Lake Erie tributary. The model design was aimed to specifically address the fact that many tributaries to the Great Lakes are dredged periodically for navigation, and that resultant changes in morphology and hydraulics can have significant impacts on DO. Due to the greater depths caused by dredging, river velocities slow considerably and vertical mixing is not as effective, leading to thermal stratification and potential short-circuiting of warmer upstream flow. The model solves the two-dimensional (laterally averaged) hydrodynamic and mass balance equations to simulate transport and transformation relevant to dissolved oxygen using an alternating direction, implicit finite difference method. Effects of oxygen-demanding pollutants from municipal and industrial discharges and also from nonpoint sources are included. A model application was developed for the Black River (Ohio), a tributary of Lake Erie. The river is dredged periodically, becomes stratified during the low flow summer months, and is affected by changing lake levels associated with seiching in Lake Erie. After calibration and confirmation, the model was used as a diagnostic tool to understand the impact of various loading sources on low DO levels observed along the bottom of the river. It is shown that sediment oxygen demand (SOD), combined with the river hydraulics, is the primary cause for low DO levels in the Black River.