Extreme heat causes fish kills in SWLA

Published: Aug. 10, 2023 at 9:51 PM CDT
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LAKE CHARLES, La. (KPLC) - The excessive heat continues taking a toll not only on us but on local wildlife as well.

Some of the most common calls fishery management agencies receive from the public are reports about dead or dying fish in a body of water, known as fish kills. In Louisiana and other areas of the Southern United States, fish kills occur most frequently in the summertime.

The most common cause of summertime fish kills is low levels of dissolved oxygen in the water. Fish need oxygen to survive, and almost all fish get their oxygen from the water.

“Hot water carries less oxygen than cooler water, so we have a lower carrying capacity of oxygen and hot water,” said Louisiana Wildlife and Fisheries Senior Technical Advisor Robby Maxwell.

Warm water is less dense and holds less dissolved oxygen than cool water. As a result, fish have to work harder to obtain oxygen in warm water.

“We’re already kind of on the edge of anoxic conditions, or hypoxic conditions and oftentimes something flips out over the edge, whether it’s multiple cloudy days, extreme heat like we’ve been having, a storm that rolls through,” said Maxwell. “Whenever that happens, you can have a fish kill that follows up, basically, there’s enough oxygen in the water.”

They also require more oxygen because their metabolism speeds up in warm temperatures.

“The recent fish kill, the menhaden kill that was in Contraband Bayou, was on a hot day, and we had a storm roll through with high winds and maybe a little bit of rain,” said Maxwell. “A lot of times that wind will stir up bottom sediments that have very little oxygen and they’re anoxic and you can stir that up and create just a lack of oxygen in the water. "

During extreme heat and drought when water levels fall and water temperatures increase, the demand for oxygen exceeds available oxygen and fish kills can occur.

“And the fish that we saw dying the other day were menhaden, which are very sensitive to low oxygen conditions,” said Maxwell. “So they’re usually the first fish to die and it’s predominantly around Lake Charles, what we see this time of year in a fish kill is a menhaden kill.”

Louisiana Wildlife and Fisheries urges anyone who sees a fish kill to report it. you can contact LDWF at 800-442-2511 or visit wlf.louisiana.gov.