In 1977, several years after these plants ceased operations, the area was again cored. Analyses showed that recent deposits were covering the highly contaminated sediment with a thin layer of new sediment that had mercury concentrations approaching background levels, thus the contaminated are being isolated and removed from the aquatic environment. Mercury in fish of Lake St. Clair and western Lake Erie was a major contaminant problem in the early 1970s. The rapid environmental response subsequent to the cessation of the point source discharges at Sarnia, Ontario and Wyandotte, Michigan can be attributed to rapid flushing of the St. Clair-Detroit River system and the high load of suspended sediment delivered to western Lake Erie, which, once deposited, covers the contaminated sediments greatly reducing the entry of mercury into the Lake Erie food chain. By 1981, only four beaches were closed throughout the year, eight were open for restricted use, and 76 were open as safe, uncontaminated beaches.
Records show continued improvement in public swimming areas.
The annual sport angler harvest of fish in the Ohio waters of Lake Erie has increased from 1.4 million pounds in 1976 to 10.1 million pounds in 1982, an increase of 621percent. The abundance of walleye within western Lake Erie also increased dramatically from 1970 to 1982. Since 1982, the fishable population in western Lake Erie has averaged over 20 million walleye. Data from 1977 through 1983 indicate the mean concentrations of total PCB in walleye exceed the Canada-United States Water Quality Agreement objective of 1.0 ppm for whole fish samples. But the mean concentrations are under the U.S. Food and Drug Administration limit of 2.0 ppm for human consumption.