‘Winter Kill’ Takes Toll On Fish At Glenwood Lake Park

The winter has taken a toll on the fish population at Glenwood Lake Park.

A representative from the Iowa Department of Natural Resources said Monday that hundreds and maybe even thousands of oxygen-deprived fish have died in the park’s main lake this winter. The dead fish began surfacing along the shoreline last week as warm temperatures melted snow and ice off the water.

“It was a winter kill event that occurred underneath the ice,” said Bryan Hayes, a fisheries biologist with the DNR’s Cold Springs Fisheries Management Office in Lewis. “The water level is definitely a contributing factor. We went into the winter low, almost all of our ponds and lakes in the region were low because of the dry end of the summer and the dry fall.”

Hayes said the lake has a maximum depth of 8-10 feet and an average of 4-5 feet. The water level  had fallen to half that amount by the end of December when ice began to form on the surface of the lake.

“You take a couple feet of water off the top of a lake like the Glenwood Park pond, that’s a significant portion of the water volume,” Hayes said. “When you remove that portion of the water volume and put ice on top of it, followed by snow cover for an extended period of time, you’ve eliminated light penetration and production of oxygen through plants. The available oxygen eventually gets used up, either through decaying plant matter or there is some consumption of oxygen through the fish population itself.”

Hayes said a representative from his office visited the park on Monday to make an initial assessment of the situation. A more extensive evaluation will be made next month.

“He’ll kind of get an idea of the extent, species and different sizes involved – just gather a little data on it,” Hayes said.

“When things warm up in April, we’ll get in there with some sampling equipment to make a determination of what species survived, what we think will repopulate on their own versus what we think we need to restock to reestablish a population.”

Because of its shallow nature, Hayes said the lake is prone to winter fish kill events. Three have occurred at the lake in the past 10 years. He added that a pond in Cass County experienced a similar fish kill this winter because of low water levels. 

“We have another one going on in a Cass County pond where the ice just came off over the weekend and we’re just discovering it,” he said.  “There are others and we’ll probably hear of more as the ice kind of erodes.”

The DNR has assisted in stocking the lake with a variety of fish species over the past several years, including large-mouth bass, bluegill, catfish and crappie. Bullheads, not introduced by the DNR, have also been identified in the lake. Hayes said the DNR will oversee the restocking process, but the fish population won’t bounce back right away.

“We will get that pond going again for folks as soon as possible but this is a setback for 6 months or a year,” he said.

“We’ve seen it bounce back from events like this before.

“We have a goal of re-establishing the fish population and providing recreation within that park. We’ll do the evaluation early this spring and then formulate a restocking plan.”

The costs associated with restocking the lake will be absorbed by the DNR.