(Connection of the Okobojis -- Community First Broadcasting Staff Photo)Spirit Lake, Iowa (Sioux County Radio) — Extremely high water temperatures across the Iowa Great Lakes may be contributing to fish kills and could cause delayed mortality among several popular game-fish species.
Mike Hawkins, Northwest Regional Fisheries Management Supervisor for the Iowa Department of Natural Resources, told reporters last week that surface temperatures exceeded 80 degrees this summer. Readings reached the mid-80s, including one measurement above 87 degrees on Big Spirit Lake.
Fish Kill Reported in Templar Lagoon
A fish kill is occurring in Templar Lagoon on the west side of Big Spirit Lake. Hawkins said the DNR has been seeing gizzard shad in greater numbers.
Disease following a large gizzard shad spawn could also be a factor. Hawkins said the deaths may represent a natural correction after the recent increase in shad numbers.
A significant blue-green algae die-off can reduce oxygen levels in the water and, in extreme cases, cause fish to die.
Effects Could Continue as Water Cools
Hawkins said water temperatures above 80 degrees place significant strain on fish. The effects are not always immediate and may continue even after temperatures begin falling.
Yellow perch, northern pike and walleye — all cool-water species — are among the most susceptible to high temperatures. Hawkins said delayed mortality among those species remains possible through the rest of August.
It is unclear whether this summer’s temperatures set a record because historical water-temperature data was not readily available. However, Hawkins said he does not recall seeing readings this high.
Cool-water fish can begin experiencing severe stress around 80 degrees. Hawkins said cooler air and water temperatures would help relieve some of that pressure.
