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Pollution

The first U.S. Clean Water Act, passed by a Congressional override after being vetoed by U.S. President Richard Nixon in 1972, was a key piece of legislation, along with the bi-national Great Lakes Water Quality Agreement signed by Canada and the U.S. A variety of steps taken to process industrial and municipal pollution discharges into the system greatly improved water quality by the 1980s, and Lake Erie in particular is significantly cleaner. Discharge of toxic substances has been sharply reduced. Federal and state regulations control substances like PCBs. The first of 43 " Great Lakes Areas of Concern " to be formally "de-listed" through successful cleanup was Ontario's Collingwood Harbour in 1994; Ontario's Severn Sound followed in 2003. Presque Isle Bay in Pennsylvania is formally listed as in recovery, as is Ontario's Spanish Harbour. Dozens of other Areas of Concern have received partial cleanups such as the Rouge River (Michigan) and Waukegan Harbor (Illinois).

Phosphate detergents were historically a major source of nutrient to the Great Lakes algae blooms in particular in the warmer and shallower portions of the system such as Lake Erie, Saginaw Bay, Green Bay, and the southernmost portion of Lake Michigan. By the mid-1980s, most jurisdictions bordering the Great Lakes had controlled phosphate detergents. Blue-green algae, or cyanobacteria blooms, have been problematic on Lake Erie since 2011. "Not enough is being done to stop fertilizer and phosphorus from getting into the lake and causing blooms," said Michael McKay, executive director of the Great Lakes Institute for Environmental Research (GLIER) at the University of Windsor. The largest Lake Erie bloom to date occurred in 2015, exceeding the severity index at 10.5 and in 2011 at a 10. In early August 2019, satellite images depicted a bloom stretching up to 1,300 square kilometres on Lake Erie, with the heaviest concentration near Toledo, Ohio. A large bloom does not necessarily mean the cyanobacteria... will produce toxins", said Michael McKay, of the University of Windsor. Water quality testing was underway in August 2019.