By Louie Stout

In early August, a fish kill on Clear Lake got anglers riled up and many were quick to blame weed treatments.

Overzealous chemical treatments can – and have – led to fish die-offs.

But that wasn’t the case at Clear Lake this summer, says Indiana DNR Fisheries Biologist Matt Horsley, who investigated the die-off of about 500 fish.

Horsley said 95 percent of the dead fish he saw were rock bass while a few crappie, bullhead and a couple of bass accounted for the remaining carcasses.

“There was a sizable weed treatment in early June and 1/10th of an acre was treated in the Marina Basin July 26,” Horsley said. “When we see fish kill that are directly caused by chemical applications it will have an immediate impact on the fish.”

Instead, Horsley believes the kill was caused by depleted oxygen overnight in a large weedy flat nearby. Rock bass like to lounge and feed in shallow vegetation after dark.

During hot periods of the summer, as was the case that time, large flats with vegetation consume oxygen at night rather than produce it as they do during the day. As oxygen depletes, fish that utilize that area get trapped and can die.

“Sediment turnover adds to the issue,” Horsley said. “When you have a lot of boating activity during the day like that lake does, boats driving over those shallow flats lifts organic matter into the water column and that depletes oxygen as well. Not only are the plants using the oxygen but decomposition of all that organic matter uses oxygen as well.”

Horsley noted that wake boats – that have gained huge popularity among pleasure boaters - are especially effective at churning up layers of bottom sediment.

“If we have a couple of days with cloud cover and no wind, it’s not uncommon for those shallow, vegetation areas of lakes to lose oxygen like crazy,” he added.

Indiana’s permit process is monitored much closer than Michigan, where fisheries biologists have little say in the matter and there is very little oversight.

Hoosier biologists often “red flag” some lakes where they believe chemical applications need to be even more tightly controlled. They ask to see the permit and will make a site inspection to insure the treatment is necessary.

Large scale chemical plant treatments for non-native invasive control in Indiana are typically limited to the year. Some private shoreline treatments are granted on a case-by-case basis.

DNR Licensing and Permits Supervisor Linnea Petercheff, who handles those permits, says Indiana limits the amount of acres that can be treated. On lakes with little or no vegetation, and lakes with trout, cisco or other endangered species, the DNR is even more restrictive.

Horsley said that just because you see an applicator on a lake doesn’t mean he’s treating it. Make sure you see him applying chemicals before sounding the alarm.

“Applicators who use state funding are required to do plant surveys, so you may see them driving and looking at the bottom or tossing a rake and pulling it in to determine the kind of vegetation on the bottom,” said Horsley.

However, he said, that doesn’t mean all applications are being done by the book. Petercheff says the DNR has prosecuted applicators whom they caught working outside the parameters of a permit or with no permit at all.

“If you think you see an illegal application, contact law enforcement and get them out there to investigate,” says Horsley.