Last year, Lake Superior water levels receded to their lowest in 77 years before rebounding, and the report by the Healing Our Waters-Great Lakes Coalition predicted global warming could lower lake levels by up to 3 feet (1 meter) over the next century.

The lower levels will hamper lake shipping, expose polluted sediments, and further damage water quality.

"Climate change is threatening the health of the Great Lakes and jeopardizing efforts to restore them," the coalition's Jeff Skelding said in a teleconference.

The coalition represents groups including zoos, fishing and hunting interests, business organizations and environmental groups.

The report said global warming added to the urgent need for the US Congress to act on more pieces of a $20 billion Great Lakes restoration plan, proposed back in 2005.

Spending priorities are billions of dollars needed to repair antiquated sewage treatment plants as well as cleaning up toxic sediments from past pollution, restoring coastal wetlands that naturally cleanse pollutants and stopping invasive species of fish, plants and mussels, the report said.

Scientists studying climate change have predicted more frequent droughts that will hurt the lakes' coastal ecosystem coupled with more intense storms that produce runoff containing toxic metals, viruses and other pollutants, the report said.

THIRSTY WORLD

The report blamed warming temperatures for ruining ice fishing in many areas, shortening the snowmobile season and harming Michigan's tart cherry crop. Warming could expand or create new oxygen-depleted "dead zones" in the lakes caused in part by uncontrolled algae growth and other processes.

"If Congress delays in acting to curb global warming and to restore the lakes, the problems will only get worse and the solutions more costly," Skelding said.

Perhaps the most promising avenue for new funding is contained in a proposal in Congress that calls for auctioning off permits to emit greenhouse gases in a so-called cap-and-trade system. Proceeds from the auctions could provide a stream of up to $3 billion a year for ecological restoration, said Andy Buchsbaum of the National Wildlife Federation.

Meanwhile, eight US states and two Canadian provinces bordering the lakes should enact a compact to prevent diversions of lake water to an "increasingly thirsty world," Buchsbaum said. All but three states have passed the compact, after which the federal governments of both countries would be asked to ratify it.