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By the 1960s and 1970s, the increased pollution caused frequent algal blooms to occur in the summer. These blooms killed large numbers of fish, and left decomposing piles of filamentous algae and dead fish along the shores. At times the blooms became so thick waves could not break. Fish-eating birds such as osprey, bald eagle and cormorant were being poisoned by contaminated fish. Since the 1960s and 1970s, environmental concerns have forced a cleanup of industrial and municipal wastes. Cleanup has been accomplished through better treatment plants, tighter environmental regulations, deindustrialization and increased public awareness. Today, Lake Ontario has recovered some of its pristine quality; for example, walleye, a fish species considered as a marker of clean water, are now found. However, regional airshed pollution remains a concern. The lake has also become an important sport fishery, although with introduced species (Coho and Chinook salmon) rather than the native species. Bald eagle and osprey populations are also beginning to recover.