The St. Louis River and Lake Superior contain elevated levels of several toxic substances, including mercury, resulting in fish consumption advisories for the presence of mercury and PCBs (polychlorinated biphenyls). Advisories based on mercury exist in Wisconsin (for walleye in the St. Louis River, Superior Bay and Lake Superior) and Minnesota (for bluegill, crappie, pumpkinseed, bass, perch, bullhead, catfish, redhorse, sucker, northern pike, walleye, and sauger in the St. Louis River).
In spite of local efforts to reduce mercury, it remains a problem. One reason is that the primary source of mercury pollution to the Lake Superior basin is from air deposition. A number of air emission sources exist within or near the basin, and an unknown but large percentage is carried to Lake Superior in the atmosphere from sources outside the basin. In addition, contaminated sediments still contribute mercury to the water column. Finally, it is unclear how much mercury still makes its way into the water from runoff or other sources that have not yet been identified.
The TMDL provisions of the Clean Water Act provide a method to address pollution problems that remain after point source discharges have met water quality standards.
The TMDL project will identify as many sources of mercury to the St. Louis River as possible, calculate the amount of coming from each one and identify ways to reduce it.
Progress will be measured several ways. In the long term, by decreased mercury level in the waters of the St. Louis River, river organisms and fish tissue. In the short term, by commitments and actions taken by individual sources, such as changes in feedstock, fuels and practices that we know will help reduce mercury releases.
Key Partners in Creating the TMDL Mercury Reduction Project:
Minnesota Pollution Control Agency
National Wildlife Federation
Western Lake Superior Sanitary District
Wisconsin Department of Natural Resources
St. Louis River Alliance
U.S. Environmental Protection Agency (EPA)