MARYLAND HEIGHTS, Mo. — "There is something seriously wrong at Creve Coeur Lake," a 5 On Your Side viewer recently told the station. Conservationists said they were right but for the wrong reasons.
The viewer described "massive" amounts of dead fish currently littering the lake's waters and shore, coupled with a "rancid" smell. The viewer isn't alone in their plight. Multiple people on the St. Louis subreddit have also recently complained about the aquatic carcasses pilling up on the Maryland Heights' body of water over the past few months.
Many more dead fish are likely baked into the lake's future, according to the Missouri Department of Conservation. The most recent fish carcasses were the bodies of approximately 70 invasive carp that died during a research study focused on eradicating the species.
"These mortalities were the result of research activities that the U.S. Fish and Wildlife Service and the U.S. Geological Survey conducted last week on the lake as part of a study on removing these invasive fish from the lake," MDC spokesperson Dan Zarlenga said. "The research consisted of heavy-duty electrofishing to capture the carp, then intensive studies and volumetric measuring to obtain data from the specimens … to help inform future eradication efforts."
The dead fish shouldn't be mourned. Invasive carp have been an ongoing problem for MDC and other conservationists along the Mississippi and Missouri rivers for decades. The fish deplete aquatic food sources, leaving native fish starving, and also cause issues for boaters by getting caught in their motors and seriously injuring passengers.
It's not the first time invasive carp infested the lake. A massive eradication effort in 2018 removed around 80% to 90% of the lake's invasive fish population, according to MDC Fisheries Biologist John Schulte.
COVERAGE FROM 2018: 47,000 Asian carp removed from Creve Coeur Lake
The 2018 effort was deemed successful, until around a year later when flooding from the nearby Missouri River reintroduced numerous invasive carp to the lake. That reintroduction led to recent mass fish kills, or fish die-offs, consisting of around 1,000 invasive carp dying at once, signaling the need for new mass removal.
"Recent fish kills consisting exclusively of invasive carp … led to us reaching back out to our partners and basically restarting a new phase of carp control efforts by estimating what the carp population at Creve Coeur is," Schulte said. "This is all geared towards figuring out how many (carp) are in the lake and generally how big they are with an eye towards a future removal effort."
Officials don't yet have a solid date on when this future removal effort will take place but will have a better idea once the data they gathered is analyzed. Schulte said once an exact day and time is selected, a notice will be sent out to surrounding communities.
Electrofishing, the practice recently implemented by federal researchers, was used specifically to study the carp population before the big removal. The practice involves a boat outfitted with long, wand-like poles and dangling cables that give off an electrical current around 5 to 7 feet from each pole and 6 to 7 feet deep into the water, according to the Virginia Department of Wildlife Resources. Electrofishing is illegal except for research purposes.
The shock stuns numerous fish in its radius, causing them to float to the surface and allowing scientists to effectively monitor the fish population's health. The shocking practice, coupled with recent severe heat, reportedly led to the lake's most recent fish deaths.
"(The fish) were returned to the water in a highly stressed condition," Zarlenga said. "That, plus the usual stressors this time of year (high water temps and low O2 levels) caused their mortality."
