RUTHVEN - Citizen reports of a fish kill at Lost Island Lake over the past weekend have prompted an investigation by the Iowa Department of Natural Resources. The fish kill appears to affected only walleyes.
According to Mike Hawkins, Fisheries Management Biologist for the Iowa DNR's Fish Hatchery at Spirit Lake, officials were notified early Sunday, Sept. 29 of the discovery of large walleyes washing up on the shores of Lost Island Lake north of Ruthven. DNR investigators responded to the lake, where they counted 74 walleyes, mostly very large fish with some approaching 10 pounds, dead along the shoreline. The majority of the walleyes, especially the largest females, had extensive amounts of fungus present on their bodies and in and around their mouths.
"This leads us to believe that they may have been under stress for some time and may have had an underlying bacterial infection," explained Hawkins.
According to Hawkins, bacteria that cause fish disease are common in the environment, however, they become an issue when the bacteria are combined with other stressors leading to fish kills. Lost Island Lake, like many lakes in the area, experienced very warm water temperatures in late summer and early fall. Normally, walleyes prefer cooler water temperatures, and become stressed in warm water, with larger fish being more likely to experience the greatest impact. The onset of a bacterial-fungal infection probably occurred around this time and culminated late last week with rapidly changing weather conditions, according to the investiation by the DNR.
"All of the walleyes we looked at on Sunday had been dead for more than a day so we hope the worst of the fish kill is over," Hawkins said. "We will continue to check in to see if the numbers increase. Cooling temperatures should help ease stress on the walleyes."
Hawkins said he talked to many concerned Lost Island area residents Sunday and received a number of calls again Monday morning. "With the relatively low number of fish, this kill will not impact the fishery. But, it's just hard to see such big fish lying dead on the shoreline."
Bacterial infection in fish cannot cross over to humans and there is no threat to eating fish of any species caught from the lake as long as the fish is prepared and cooked properly.
Hawkins said the DNR investigators did also find two dead northern pike on the south shoreline, Sunday, but it was difficult to tell if their deaths were related to the investigation.