Lake St. Clair Coastal Habitat
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Toxic/Chemical Loadings


Photo: Wisconsin DNR

Toxic chemicals can stress the environmental health of the Lake St. Clair coastal habitat. They enter the system through a variety of pathways, including both point source discharges and nonpoint source runoff. Contamination from historical practices also continues to stress the environment. While the passage of stringent laws and regulations have led to declines in discharges of toxic chemicals, many still persist in the system and are available to plants, fish and wildlife.


Toxic chemicals can negatively impact the health and reproduction of animals. They have had the greatest impact on animals at the top of the food chain, such as predatory birds, fish, and mammals. Contaminants become more concentrated as they move up the food chain through the processes of bioaccumulation and biomagnification. Some of the effects that have been documented include thinning of egg shells and deformities among Great Lakes birds that prey on fish, and lower hatching success and increased deformities in snapping turtles with high contaminant concentrations. Road salt runoff is also a concern as it has been shown to alter algal, macrophyte and faunal communities of wetlands.

Both point and nonpoint sources of pollution contribute toxic contaminants to the environment. Point sources include industrial discharges, effluent from municipal wastewater treatment plants and waste disposal sites. Nonpoint sources of chemicals include land runoff, contaminated sediments and airborne deposition. Areas of Concern in the Great Lakes basin also serve as a source for toxic chemicals. Point source discharges from industry are generally well regulated in the study area. However, they have the potential to stress the environment if there is an accidental spill , runoff or leakage, or if they are discharging low levels of pollutants that can cause stress over time. Accidental spills along the St. Clair River corridor have been a problem in the past. However, the number and size of spills or releases has reduced dramatically over the last several years due to measures implemented by both U.S. and Canadian industries. On-going monitoring must continue to assure that the number of spills and the quantity of materials spilled continues to decline. Nonpoint sources are more difficult to regulate and in many areas may be the primary source of current contamination.

Contaminated sediments from historic industrial activities are a likely source of many toxic pollutants measured in fish within the Lake St. Clair coastal habitat . There are two AOCs in the study area: the St. Clair River and the Clinton River. Efforts are underway at both sites to remediate past contamination . However, ongoing contamination, such as stormwater runoff, and accidental release of toxic substances continues to cause sediment and water quality degradation in these areas.

Other point sources, such as municipal wastewater treatment plants and waste disposal sites are also a concern. Municipal wastewater treatment plants may discharge low levels of metals and organic pollutants from treated industrial waste and household chemicals. Even when in compliance with regulated guidelines, these facilities can contribute substantial loads into the Lake St. Clair system over time. Though well regulated, waste disposal sites can potentially contaminate the environment through surface runoff or seepage into groundwater. Historic dumping sites and abandoned landfills, although presently not quantified, could be a significant source of contamination to the region.

Pesticides, including insecticides, algicides, fungicides, herbicides and rodenticides are an environmental concern because they often end up in waterways via stormwater runoff. These contaminants can have lethal and sublethal effects on fish and wildlife, affect species reproduction, impact the food supply, alter habitat and affect productivity. Airborne deposition, is also a source of contaminants, particularly mercury, to the region. Airborne deposition directly to the St. Clair River represents a minor source because of the small surface area relative to its very large flow. However, inputs from Lakes Huron, Michigan, Superior and their watersheds can be significant due to their large surface area. Atmospheric contamination of water in Lake Huron directly affects water quality in the St. Clair River and Lake St. Clair.

For more information, see: Coastal Habitat Plan, Section V (PDF)