TOPEKA (KSNT) – Have you noticed lots of dead fish in your local pond or lake this summer? Kansas wildlife officials may have some answers for you.
You may have heard the term “fish kill” at some point, which refers to mass die-offs of fish in bodies of water. Wildlife and health experts say there are many possible causes for these events, which can leave dozens or even hundreds of dead fish floating at the surface of local lakes and ponds, but the change in season could hold the answer for some Kansans noticing the phenomenon.
The Kansas Department of Wildlife and Parks (KDWP) explained in a recent social media post that it receives numerous calls each year as summer transitions to fall of dead fish popping up in people’s ponds. The agency points to the change in temperature that comes with this transition, summer heat replaced by cooler fall air, as one of the primary reasons people may see a fish kill.
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“In the summer months, ponds and lakes stratify or form layers based on the density of the water. The water closer to the surface is warmer and less dense due to sunlight penetration and wave mixing. The water at the bottom is cooler and denser. Because these two layers have different densities, they do not mix (envision oil and water). As a result, none of the oxygenated water from the upper layer mixes with the bottom layer leaving the bottom of your pond or lake anoxic during the summer months. Throughout the summer dead material from fish, algae, and plants will continue to fall to the bottom unable to get broken down due to the lack of oxygen.”
KDWP social media statement excerpt
The KDWP said the shift to cooler temperatures causes the bottom layer of water to mix with the upper layer, causing undecomposed material to get broken down by bacteria that start to multiply at a fast pace. The rapid increase in bacteria causes a drop in the oxygen level in the water which fish need to survive, resulting in a fish kill.
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A similar event happens as winter transitions to spring but typically doesn’t result in as many fish deaths, according to the KDWP. While some ponds and lakes are hit annually with fish kills caused by weather changes, others may only experience these events infrequently.
The KDWP recommends that pond owners who experience a fish kill should wait a few weeks before checking the water to see what fish are left and consider restocking. The agency also recommends adding water circulation to backyard ponds in the form of an air diffuser or pumping in fresh water to reduce the chances you’ll experience a fish kill.
Mass fish die-offs in the summer are often referred to as “summerkills” by the KDWP. If you notice fish in the pond or lake sitting at the surface and gulping for air, a summerkill may be imminent.
Fish kills can also be caused by pesticides, diseases and parasites, according to the KDWP. You can learn more about fish kills in Kansas by clicking here.
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