Warm, low water wreaking havoc on fish

As even rust and weeds grind to a halt in Iowa's newfound desert climate, rivers and streams slow to a trickle of water too warm in some cases to support aquatic life.

A $10 million fish kill last week on the lower Des Moines River has been attributed to 97-degree water that parboiled more than 37,000 shovelnose sturgeon in a 42-mile stretch.

Department of Natural Resources fisheries biologist Mark Flammang said the water temperature registered at least 97 degrees at every site sampled.

“You just don't see rivers at 97 degrees,” he said.

About 100 walleyes died of heat stress last weekend at the upper end of Coralville Lake, according to DNR fisheries biologist Paul Sleeper.

With stream flows continuing to fall, while temperatures are expected to climb well into the 90s next week, fish will remain vulnerable to hot water, low levels of dissolved oxygen and chemical contamination, Sleeper said.

“The hotter the water, the less oxygen it can hold. The lower the flow, the less water to dilute contamination,” Sleeper said.

Sleeper said he also is concerned that the drying up of smaller streams forces the minnows and smaller fish that reside there to move farther downstream or perish.

The majority of the state's 180 river gauges are registering low flows, according to Dan Christiansen, a hydrologist with the U.S. Geological Survey in Iowa City.

The Iowa River at Iowa City is flowing at 9.22 percent of its normal summer rate, and the Cedar at Cedar Rapids is at 11.23 percent of summertime normal, Christiansen said.

“These extremely low flows typically occur in late August and early September. They are much earlier than usual this year,” he said.

The Cedar at Cedar Rapids registered a temperature Thursday of 84 degrees.

Lake Macbride in Johnson County and Pleasant Creek Lake in Linn County are only an inch or two below their normal levels, but Clear Lake in north-central Iowa has dropped 18 inches, according to Sleeper.

In 1988, the year of Iowa's last major drought, Clear Lake fell 40 inches and took several years to regain the lost level, he said.

Spring-fed trout streams in Winneshiek and Allamakee counties are maintaining normal flows with water cool enough to sustain the fish, said DNR fisheries biologist Bill Kalishek.

Trout streams farther west in Howard and Mitchell counties have warmed to more than 70 degrees, and hatchery personnel are measuring stream temperatures before stocking, Kalishek said.

“If they find water over 75 degrees, they bring the trout back to the hatchery,” he said.