MDC investigates reported fish kill at Ray Behrens, Spalding, and Dam portions of Mark Twain Lake

HANNIBAL, Mo. – The Missouri Department of Conservation (MDC) received several reports late last week of a walleye fish kill event at Ray Behrens, Spalding, and Dam portions of Mark Twain Lake. An investigation into the reports revealed that this was likely a natural fish kill event, and that there is no toxic pollution involved.

Fish kill events can occur naturally in Missouri, and they are classified as the sudden death of fish that occurs in a lake or stream. Each year, MDC handles around 100 fish kills and other water quality events that pose a threat to fish, wildlife, and recreation. Of these events, 75-80% are caused by natural conditions, as is the case with this fish kill at Mark Twain Lake. The rest of these events are caused by pollution, chlorinated drinking water, or chemical spills that contaminate the waterways.

In this particular instance, the lake has experienced extreme stratification due to consistently warm weather over the past several weeks. Oxygen is only present 13-feet deep, and the water has reached 82 degrees Fahrenheit. Walleye thrive at temperatures between 55 and 70 degrees Fahrenheit and prefer water up to 30-feet deep at this time of year. Currently, walleye are being forced to choose between water that is too warm or too low in dissolved oxygen, making it difficult for them to survive. Events like this are not uncommon at Mark Twain Lake during periods of drought and warmer temperatures when dissolved oxygen levels in the water are at risk of dropping. The last walleye fish kill occurred in 2022.  However, these situations pose no environmental threat to humans.

In the aftermath of a fish kill, nature will take its course and allow the decomposition process to take place. Nutrients from this process will be fed back into the ecosystem, benefiting the local plants and animals. While this may not be a pretty sight to look at, it is best for the environment to let the process run its course. Any living fish in the area are safe to catch and consume.

MDC asks that the public reports suspected fish kills here: https://short.mdc.mo.gov/4PV or that they talk to fisheries biologist, Annie Hentschke at 573-248-2530 as she is actively tracking this event.