Dam failure changes conditions for Maquoketa River wildlife

Even fish can get too much water.

Last weekend's record flood reshaped the Maquoketa River and scattered its denizens into unfamiliar and hostile environments, said Department of Natural Resources fisheries biologists.

“It will be the end of the line for a lot of the largemouth bass, crappies and bluegills that had been living in Lake Delhi,” said DNR fisheries management biologist Dan Kirby.

The failure of the Lake Delhi dam on Saturday instantly transformed the lake into a river, imperiling fish species that prefer the slower current of an impoundment, said Karen Osterkamp, the DNR's northeast Iowa fisheries supervisor.

While channel catfish and smallmouth bass will adapt well to their new surroundings, the sudden transition to a river environment will likely be too much for the largemouth, bluegills and crappies to overcome, she said.

The release of incalculable tons of sediment that had collected on the bottom of the 81-year-old lake also will harm the world-class smallmouth bass fishery in the 4.5-mile catch-and-release river section directly below the dam, Kirby said.

The rocky riverbed there provides an ideal setting for smallmouth to reproduce and thrive, but silt deposits will likely degrade their environment, Kirby said.

“It's kind of uncharted territory - the volume of sediment that will be flowing into that area - and in some respects it is a worst-case scenario,” he said.

Greg Gelwicks, the DNR's rivers and streams research biologist, said the sediment will continue to flow downstream for months or years.

The “head cut” process, in which the flowing river carries away the soft material from the former lake bed, is clearly visible above the breached dam. “It will look like an underwater waterfall as it works its way slowly upstream,” Gelwicks said.

Whatever happens, the DNR will be able to document it because the catch-and-release zone contains one of the most studied bass populations in the state, Kirby said.

“I'm sure there will be negative impacts, and census work this fall will give us a good idea of its extent,” he said.

The young fish are the most vulnerable to the powerful currents that swept downstream after the dam failure, said Manchester Hatchery supervisor Dave Marolf.

“People think everything has been washed away, but that's not the case in a riverine system. Fish like water, and most of them can handle it pretty well,” Marolf said.

Parts of the riverbed itself will have been reshaped by the forceful currents, and debris from upstream will litter the river corridor, the biologists said.

The dam failure will not affect the spread of the zebra mussels that have colonized the lake, said Kim Bogenschutz, the DNR's aquatic invasive species program coordinator.

“They were already downstream of the dam,” she said.

Most of the zebra mussels in the lake have lost their water cover and will die, and their rate of reproduction will be slowed, Bogenschutz said.

“They are basically a lake species and need calmer water to thrive,” she said.

DNR fisheries personnel generally favor the removal of dams, which obstruct fish movement and impair fish habitat and water quality in the impoundments they create. In the case of the Delhi dam, which officials have pledged to rebuild, Osterkamp said they understand that the social and economic interests of the hundreds of affected lakeshore residents will take precedence.

“We hope to see some collaboration to do what's best for people and fish and the environment,” she said.