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that around 10 to 15 lakes across his territory have been affected. He said predicting which lakes might be affected is difficult but that the most vulnerable lakes tend to be shallow -- less than 7 feet deep.
• Warm water naturally holds less oxygen. Lauer said high algae levels common in summer also deplete dissolved oxygen supplies and so does competition from hardier carp and bullheads.
• Fortunately, enough fish usually survive the summer die-offs to repopulate affected lakes, he said.
• Drewes said he wouldn't be surprised to see die-offs of ciscoes (also known as tulibees), whitefish and suckers later this summer in his area. Those fish are sensitive to temperatures and oxygen levels, too.
• Biologists and anglers in the region worry more about winter fish kills, which hap

pen much more often than summer die-offs. Oxygen available for fish is limited when snowfall blocks light into the lakes, preventing photosynthesis. Plants die and stop giving off oxygen, and then the plants consume oxygen as they decompose.
• In Wisconsin, DNR fisheries biologist Ryan Koenigs said his department started seeing mostly bigger northern pike dying on shallow southern lakes that had water temperatures in the upper 80s and 90s late last week. The La Crosse River Marsh also saw a significant die-off.
• State officials also have seen dead carp, yellow perch, bluegills, largemouth bass and gizzard shad, he said. Some of the dead fish could be attributable to blue-green algae but the water temperature was the biggest factor, he said.
• Those kills are not expected to have an impact on the overall populations but will likely affect the 26-inch and bigger adult northern pike prized by anglers. Most of the fish that died in Wisconsin were bigger than 20 inches and some were bigger than 40 inches, Koenigs said.
• "It's just kind of sad to see these large northern pike dead. These fish are probably 15 years old, if not older," he said.
• The die-off of northern pike between 2 pounds and 10 pounds in the James River came as a particular disappointment to North Dakota Game and Fish Department fisheries chief Greg Power, who said the James had been above flood stage for the past three years, creating ideal spawning conditions. But the river now is only about 8 feet deep in spots, which prevents the fish from diving to cooler water, he said.
• "We had never had so many pike in the James River," Power said. "Unfortunately, thousands died this year and the guys are still trying to figure out how many."

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