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How did Canada and the United States improve water quality in the Great Lakes after the 1970s?

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lake Lake Ann in North Cascades National Park, Washington, U.S., viewed from the park's Maple Loop Trail. The North Cascades National Park is a large wilderness area that preserves majestic mountain scenery, snowfields, glaciers, and other unique natural features.

Following the 1970s, Canada and the United States initiated a major cooperative effort focused on pollution control to address the environmental degradation of the Great Lakes.1

This collaborative approach was driven by the recognition that pollution had severe consequences, including the contamination of wildlife, the loss of valuable fish species, and increased costs for water treatment. Strategies to improve water quality have included the diversion of treated sewage away from the lakes in various urban areas, such as Chicago. These collective measures have successfully resulted in improved water quality and the resurgence of certain fish populations.1

International research and cooperation have remained essential to these mitigative measures, particularly as concerns regarding eutrophication and the accumulation of toxic substances have persisted since the post-World War II era.21