“They’re already at what we would have expected to be their peak temperatures for the summer, and we have several more weeks of warming to go,” University of Minnesota physics professor Jay Austin told The Detroit News.

Lake Superior commercial fisherman Ralph Wilcox told the paper that whitefish have become much harder to catch since they fled the warmth near shore for cooler, deeper waters.

Those fish that are still swimming near shore aren't biting. "It makes the fish lethargic and they stop feeding during the day," said Lakeside Fishing Shop co-owner Dan Chimelak.

This summer’s warmth also appears responsible for the unusually thick blooms of algae that have slimed some parts of the Great Lakes.

But the balmy waters have delighted many vacationers who can now swim much longer in the usually bracing surf.

Graphic Data: NOAA Satellite and Information Service