Pollution in Lake Superior

Problems

• Over the last 30 years, concentrations of nearly all measured contaminants in fish and the water column have declined in Lake Superior, with the exception of toxaphene. Between 1986 and 1997, concentrations of toxic organic pollutants in the water column declined by more than 50 percent. However, dieldrin, mercury, PCBs, and toxaphene concentrations in Lake Superior continue to exceed the most stringent water quality standards. Because of its remote location, limited industrial activity, and large surface area to watershed ratio, Lake Superior receives most of its contaminant loadings via atmospheric deposition, especially concerning PCBs, mercury, and toxaphene. Canada’s prairie provinces and the southern United States appear to be sources of lindane to Lake Superior.

• Shoreline development

  Development of the shoreline, including the construction of recreational homes, is one of the most pressing issues facing Lake Superior. For example, the Keweenaw Peninsula has seen unprecedented growth in the past 20 years with 50 percent of the homes now classified as recreational or second homes.

• Habitat loss

  Although Lake Superior's nearshore and open water habitats are of high quality and promote an abundance of trout, whitefish, and herring, habitat loss in tributaries and embayments is a concern. Most of the habitat loss in Lake Superior has occurred in these areas, including the eight Areas of Concern.
  
  These tributaries are significantly degraded by agriculture, mining, hydroelectric dams, industrial effluents, and waste, wetland dredging and filling, non-point source pollution, shoreline development, and land use practices that increase surface runoff and erosion.
  
  Habitat loss and harvest and management of select species have caused dramatic changes to wildlife communities over the past 150 years. Eighteen animal species in the Lake Superior watershed, including mammals, birds, insects, reptiles, and amphibians, are listed as endangered by the federal government. In addition, 400 species (300 of which are plants) are listed by provincial or state jurisdictions as endangered, threatened, or of special concern.

• Non-native invasive species

  Lake Superior has the highest ratio of non-native invasive species to native species of all the Great Lakes. Sea lampreys kill thousands of lake trout each year. Invasive round goby and ruffe fishes have colonized some nearshore habitats and could negatively impact the nearshore cool-water fish community. Other invasive species predicted to have significant impacts on the native community include the gypsy moth, emerald ash borer, Asian longhorned beetle, rusty crayfish, and exotic buckthorns.

• Wetland loss and degradation

  Wetlands account for 15 percent of the Lake Superior basin in the United States and up to 25 percent in Canada. The greatest threats to Lake Superior's remaining wetlands are wetland draining and filling, toxic contamination, water level regulation and site-specific stresses such as shoreline development. Other threats include invasive species and diminished water quality.

• Forest fragmentation

  Forest fragmentation and changes in forest composition are two of the seminal changes to the Lake Superior region since settlement times. In the 1880s, Lake Superior forests in the United States were almost entirely clear-cut. Aspen, birch, fir, and poplar have increased since this time while spruce and pines have been severely reduced. Forest cover is anticipated to remain the same or to increase slightly in future years. Hardwood forest fragmentation will continue to increase due to development and road construction.