Lack of oxygen leads to fish kill at Butler Lake
Officials are monitoring Butler Lake in Libertyville after hundreds of fish died after a treatment to remove unwanted vegetation.
A passer-by on Monday reported seeing a large number of dead and struggling fish in a lagoon area on the north side of Lake Street.
Approximately 400 fish, including white sucker, American shad and largemouth bass, were killed relatively soon after an herbicide designed to control invasive weeds, including an excessive growth of water lilies, was applied.
Clarke, the St. Charles-based company best known for mosquito control, also has an aquatics management unit and last week made the application in the lagoon and areas near the fishing pier and the Lake Street bridge, according to Paul Kendzior, the village's public works director.
The herbicide is registered by the Environmental Protection Agency for uses in aquatic sites, according to Laura McGowan, a company spokesperson.
An internal review including weather, protocols and procedures showed the lagoon "was likely stressed due to changes in environmental conditions," she added. That include a large rainfall, a change in temperature and a decrease in dissolved oxygen, which led to the fish kill, McGowan said.
"These conditions can lead to fish die-offs with or without the presence of herbicides and can occur throughout summer especially during drought times when a large rainfall occurs," she said.
Village crews removed hundreds of dead fish, according to the Illinois Department of Natural Resources.
"This vegetation dieback reduced the oxygen levels in these areas depriving the fish of oxygen," Kendzior said. The applications did not directly harm the fish, he said.
The IDNR was contacted by the Lake County Health Department's Lakes Management Unit, which checked the area near the pier.
"The dissolved oxygen in the water was very low," said Mike Adam, senior biologist with Lake County. "Now you clean up the dead fish and hope it wasn't extensive."
Kendzior said the IDNR also is "fully aware" of the situation.
Clarke is working with the village to monitor the health of the lake and lagoon.
"The IDNR indicates that this happens from time to time when a body of water is overpopulated with vegetation," he said. "The IDNR and the village will continue to monitor the fish variety and population."
IDNR spokesman Tim Schweizer said the agency wants to conduct a fish survey this fall.
According to Clarke's website, oxygen levels vary within bodies of water. Shallower bodies are warmer, and the warmer the water, the less oxygen available for fish.
Submerged native plants produce oxygen during the day but the process reverses at night, according to the company, so extensive coverage can stress fish populations.
A 2015 report by the Lake County Health Department showed water quality, including parameters such as nutrients, suspended solids, oxygen, temperature and clarity, in the 55-acre Butler Lake had improved from readings 10 years earlier.
The report listed coontail and white water lily as the dominant aquatic plant species.
"In general, it's a nice lake. It usually has good water quality and plant diversity," Adam said.
The village for years pursued federal assistance to dredge and restore the lake, which had grown shallow. A $3.45 million project, which kicked off in 2005, included controlling invasive species and won the 2009 Conservation and Native Landscaping Award from the U.S. Environmental Protection Agency and Chicago Wilderness.