The long stretch of hot, dry weather is causing large amounts of dead fish to show up on some shorelines.
The Wisconsin Department of Natural Resources (DNR) announced last week fish kills in four southern Wisconsin counties.
Nearly 2,000 fish, including a large number of walleye and channel catfish, were reported dead at the base of Lake Sinissippi near Hustisford in Dodge County. And another 500 fish, made up of mostly carp and walleye, died in the Rock River in Dodge County.
Two other fish kills, at Beckman Mill Pond in Rock County and the Yahara River in Dane County, are still being investigated, the department said.
Fish kills are normal for this time of year, the department said, as temperatures rise and less rain falls the water and oxygen levels in rivers, lakes and ponds decreases making it harder for fish to survive.
“As water temperatures go up, water is not able to hold as much oxygen, which fish need,” said Scot Stewart, DNR south central district fisheries supervisor, in a statement. “Respiration by plants can reduce the amount of oxygen to levels lethal to fish. That’s when summer fish kills occur.”
Stewart said in a phone interview Monday the number of fish kills depends on the amount of fish that are in the area at a given time.
“If there are a higher percentage of fish in the area at the time of a kill then a larger amount will probably surface,” he said.
Stewart added it is difficult to determine the percentage of fish killed in a body of water because of fish movement over a period of time.
“Our fish kill number will never be 100 percent,” he said. “We won’t see fish that have sunk to the bottom or lodged on roots in trees.”
Stewart said when the department gets a call about a possible kill they will send a DNR employee out to investigate.
“Sometimes we will get an exaggerated report,” Stewart said.
The department also will look at the vegetation growth and the recent temperatures of the area, he said.
Lori Williams, Rock County Parks Department director, said her office is still waiting on the final report from the DNR.
Williams said repairs to a dam at Beckman Mill County Park, west of Beloit, lowered the water level in the pond, which combined with the heat, is believed to have contributed to the fish kills there.
No reports of fish kills have occurred in Rock County since late 2007, Williams said.
Normally, fish will sink once they have died and then rise to the surface, Stewart said. Some either sink back down, remain on the surface or make it to the shoreline, Steward said.
The department does not clean up the fish, but allows the landowners to do so if they wish.
The public is urged to call the DNR Tip Line at 1-800-TIP-WDNR to report a potential fish kill, or if any dead fish are spotted.