SPRINGFIELD, Ill. — Fish by the thousands are dying in Illinois and throughout the Midwest, victims of solar-heated water and lack of oxygen in the drought-stricken rivers, lakes and ponds from Ohio to the Great Plains.

“This could be an extremely bad year for fish kills,” Dan Stephenson, fish biologist with the Illinois Department of Natural Resources (DNR), noted last Friday.

Stretches of the Vermilion River in La Salle and Livingston counties in mid-state Illinois are one example, where the deaths of several thousand fish were reported Thursday, their silvery upturned bodies floating on the surface of the water.

The incidence of heat-felled fish is not totally unusual. There are numerous kills in lakes, rivers and private ponds in a normal year, Stephenson said. “However, this is a particularly bad year for that because of the drought,” he noted.

“The fish get trapped in pools, the pools are drying up and there’s no oxygen available for them. There’s going to be a lot of this fish kill going on throughout the state. We are also losing some of the Asian carp that way; I wish we’d lose them all.”

A press release from the state of Indiana noted one benefit in that the drought is killing the invasive Asian carp in the Wabash River. Asian carp are a threat to native species; they prefer living in oxbows and backwater areas, which are drying up and leaving the carp stranded without adequate water, according to the release.

In Iowa, hot weather is being blamed for the widest-stretching fish kill in the state’s history, a published report noted. The kill occurred on the Des Moines River from Eldon to Farmington in the southeastern part of the state. According to the report, the incident killed 58,000 fish in a 42-mile length of the river last week.
 Samplings showed the water temperature at 97 degrees.

Fish kills are not affecting entire rivers, streams and lakes in Illinois. Only small stretches of the Fox, Kankakee and Mississippi rivers, the Rock River in far northern Illinois and all the way downstate to the Little Wabash River, the Big Muddy River and the Kaskaskia River are affected.

“This is going to be quite common, I’m afraid, until we can get some rain,” Stephenson said. “I’m afraid the rivers are just drying up, and these fish are getting trapped and their oxygen runs down. It’s just these small stretches of the rivers. There are other places in the rivers where the fish aren’t being bothered.”

Somewhat more affected is the Savannah area to the Wisconsin border in Illinois, where some species such as the Northern Pike and Walleyes are victims. “They are a cool-water fish, and the water has been a little too hot for them, so we have some of them dying. I’m afraid that until we get some rain, we’re going to have this problem showing up everywhere,” Stephenson said.

“The governor has a drought task force out, so I’m taking calls from everybody throughout the state. There’s not much else we can do. There’s no way to estimate the number of fish killed by the heat stress.”

Each Monday, the DNR is listing all fish kills reported to the agency, Stephenson said. Illinois Gov. Patrick Quinn has put together the drought task force to discuss the need for actions to ensure public safety and support agriculture, wildlife and natural areas, and preserving water supplies.

“We are seeing drought conditions throughout Illinois, and it is important to convene the state’s top experts on weather, water resources and water supply management, agriculture and public health and safety to address the needs of communities around the state,” Quinn was quoted as saying in a published report.

The DNR and Illinois Environmental Protection Agency are leading the task force. Members are top officials with the state departments of Agriculture and Public Health, Emergency Management Agency and the Illinois Water Survey.

The temperature of the heat in the water needed to kill fish depends on the species. “Like the cool-water fish, when the water is warmed to over 90 degrees, they’re really starting to suffer,” Stephenson said. “We’ve had some fish kills on La Salle and Braidwood lakes, and a lot of private ponds.

“There are about 90,000 private ponds throughout Illinois, and we’re getting calls from dozens of them. If they are more tolerant of warm water, they’ll live longer than the cool-water fish that won’t.”

La Salle and Braidwood lakes are manmade bodies constructed to cool and recirculate the water used at nuclear generating stations in La Salle and Grundy counties.

The fish kill problem is oxygen-related, too. As the water level is lowered through heat evaporation in the rivers, lakes and ponds, the fish become trapped in pools by rocks on the bed of the body of water and the oxygen is exhausted quickly. Hot water holds less oxygen volume per gallon than cold water.

“The amount of fish deaths could increase as the private ponds dry up throughout the state,” Stephenson said. “I received reports of fish kills from 12 to 15 ponds today alone. And, there are hundreds of ponds, and stretches of rivers and streams in Illinois.”

The dead fish are left to float on the surface of the water – they are not removed. The bodies will rot away in a week or so, and the nutrients in their bodies will go back into the water to refertilize for next year’s batch of fish.

“When rain finally arrives and the rivers build back up to their normal levels, the fish will replenish themselves,” the biologist noted. “They will come back very quickly and start reproduction again.”