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Drought’s impact on trout streams could intensify

Dave Marolf, manager of the Manchester (Iowa) Fish Hatchery, holds a net with brook and rainbow trout. The state Department of Natural Resources is slowly releasing 15,000 trout into northeast Iowa's streams because of low stream levels. (Clay Masters for Harvest Public Media)

With this year’s severe drought, media attention has understandably centered on agriculture. But there is a less-discussed ripple effect that involves fish.

In Iowa, state Department of Natural Resources numbers show stream flows are well below normal and groundwater levels are reaching historic lows. With less water, the streams heat up.

Throughout the summer, many fish across the Midwest died because of high water temperatures. When the Des Moines River reached 97 degrees in July, about 40,000 sturgeon were killed. But biologists also are concerned about the impact of the drought on cold-water streams. Some streams in northeast Iowa saw water temperatures over 80 degrees this summer, which is dangerous for trout.

“Those areas receive water almost exclusively from groundwater and the cold water holds more oxygen than other warmer water," said Iowa State Fisheries Extension specialist Alan  Patillo. "In those areas you would expect to see less pollution so they’ve sort of adapted their lifestyle to live in those pristine environments.”

Patillo said the cool-water streams in northeast Iowa are unique to the state and are home to three species of trout: the exotic rainbow, brown trout and brook trout.

Dave Marolf, manager of the Manchester (Iowa) Fish Hatchery, held back almost 15,000 of the trout because of the warm water. The Department of Natural Resources is now slowly releasing the overstock into the northeast Iowa streams.

Still, this delay didn’t slow down fisherman yet. Marolf said he expects a record-breaking 40,000 fish anglers this year. But based on past droughts, the impact may be felt in later years, he said.

"The only thing we have to relate to is history and history tells us if you go back to 1988 and ’89. For the farmers, ‘88 was much worse — they had a much poorer crop than they did in ’89. But here at the fish hatchery, we didn’t see the full effect of the drought ‘88 until ‘89 when it stayed dry,” he said.

How long the drought lasts and how much it affects the state’s fish population is hard to predict. But Harry Hillaker, Iowa’s state climatologist, said drought loves company and with this drought, there’s a lot of company.

“Nationally this has been the most widespread drought we've had since 1955, '56, so a long time since we had a drought over such a large part of the country," Hillaker said. "So that makes it hard to get out of. Everyone’s dry there’s just not as much moisture around… humidity is low it makes it harder to get a rainstorm.”