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Hot Weather Causes Fish Kills in Southeast Iowa
Posted: 07/10/2012
A section of the Des Moines River with a history of hot weather related fish kills was home to one of the longest in the state’s history with nearly 58,000 dead fish in more than 42 stream miles with a value exceeding $10.1 million.

Dead fish were found in the Des Moines River from the dam in Eldon to the Farmington Bridge on Hwy. 2.
The majority of fish killed, 37,159, were shovelnose sturgeon, with a value $116.20 per pound, according to American Fisheries Society guidelines for monetary value in fish kills. The sturgeon averaged more than two pounds each with a value of $9,865,241.85.

The investigation began around 10:30 a.m., July 7, when Lacey-Keosauqua State Park manager Justin Pedretti reported seeing “lots” of dead fish in the river to Mark Flammang, fisheries biologist for the Iowa Department of Natural Resources.

Flammang and fisheries aide Wes Alexander were joined by Jon Ryk and Paul Brant from the DNR’s Washington field office on the river at Eldon and for the next 11 hours they collected water samples, conducted fish counts, and took water temperature readings working their way downstream to Farmington.

“We didn’t find low levels of dissolved oxygen or high levels of ammonia which is usually indicative of some sort of spill so it comes down to water temperature,” said Flammang. “You just don’t see rivers at 97 degrees and it was 97 degrees at every site that we sampled. I’ve never seen water at that temperature in Iowa.”

The effects of high water temperature on fish were likely compounded by stream flows that had fallen from 5,000 cubic feet per second before July 4, to 1,200 CFS on July 7.

In addition to shovelnose sturgeon, Flammang found more than 12,000 channel catfish, nearly 1,900 walleye, more than 1,100 flathead catfish, 1,500 freshwater drum, 750 carpsuckers, 370 white bass, 45 shorthead redhorse and 25 goldeye. 

“It looks like a lot of fish, but I don’t expect this fish kill to have a noticeable impact on the fish population in this stretch of the river.  The shovelnose sturgeon is something we’re concerned about, but the river has shown time and time again that it can recover,” Flammang said.

This section of the Des Moines River has had sizable fish kills over the years, including 2006 and in 2008, during summer flows of 300 to 500 CFS and high water temperature.

The DNR also investigated fish kills in the Iowa River between the Hawkeye Wildlife Area and the Hwy. 965 Bridge in Johnson County, and in the main lake at Lake Odessa in Louisa County. 

The section of the Iowa River has periodically experienced hot weather fish kills in the past.

Paul Sleeper, fisheries biologist at Lake Macbride, said water from the shallow Hawkeye Wildlife area with low oxygen levels and temperatures in the 90s flowed under the Hwy. 965 and I-380 bridges were most of the dead fish were found. Sleeper said they counted 95 walleyes at the upper end of the Coralville Reservoir, along with six channel catfish and a few common carp on Monday. 

“It looks like they had been dead for several days,” Sleeper said.

At Lake Odessa, 96 percent of the 19,000 fish killed were gizzard shad that are susceptible to changes in water temperature. Chad Dolan, fisheries biologist at the DNR’s Lake Darling office, said they suspect the kill happened Saturday night after the high air temperatures. The water temperature was in the low to mid 90s.

Other species killed were bluegills, crappies, freshwater drum, northern pike, largemouth bass, yellow bass, common carp, channel catfish, goldfish and brown bullhead. Dolan said live fish were seen in the areas of the fish kill and anglers were catching fish during the Sunday

While elevated water temperature is likely the cause of these fish kills, the DNR will be submitting water samples for analysis to see if other factors were responsible.  If the public sees dead or stressed fish, they are encouraged to contact the DNR at 515-281-8694.