A perfect storm of high temperatures, a falling river and the return of afternoon thunderstorms caused two localized fish kills in the Atchafalaya Basin within the last week, according to a Louisiana Department of Wildlife and Fisheries freshwater biologist.

“Basically what has happened is you’ve got atmospheric temperatures that were reaching 100 degrees, so that water in those shallow swamps is literally cooking in there. It’s reaching like 85 or 90 degrees, and the warmer the water gets the less oxygen it’s able to hold,” Brac Salyers said. “So as the Atchafalaya River is starting to drop, all those flooded swamps and shallow areas that have been holding water for so long are draining out, and it’s pulling all the vegetation and inorganic material with it.

“Then we started to get storm fronts in the last few weeks. It had been dry, dry, dry — almost drought conditions in a lot of Southwestern parishes. And we suddenly started to get rain. And the cold rain helps further stir up the water, because the cold water sinks.”

Salyers explained that because cold water is denser than the hotter water near the surface, it sinks and creates more issues for already-stressed fish.

“It stirs up the water and the rotten plant material, and it further agitates the entire water column which drops the amount of oxygen available to the fish,” he said.

Shortly after afternoon storms last Tuesday, and then again this Sunday, the department started receiving calls on dying fish near the Whiskey Bay boat launch.

“The majority of the kill last week was freshwater drum. That was about two-thirds of the fish we saw,” Salyers said. “As far as the rest of them, it was across the board — everything from shad to bream, goggle-eye, sac-a-lait and bass.”

With more rain in the short-term forecast, Salyers said it’s possible additional fish kills could occur.

“It definitely seems like as long as the river continues to drop like it is, and the water is pulling out of the swamps, it’s going to be a stressful environment for all the fish that come in contact with it,” he said. “And anytime we get these strong summer thunderstorms in the afternoon, there would be the possibility of having a fish kill associated with the bad water coming out of the swamps.

“I’m not saying it’s going to happen, but it does have the potential to create an anoxic environment that would be so stressful the fish wouldn’t be able to make it.”

The good news is that with fall fast approaching, the factors that contribute to low-oxygen conditions will start to subside, and Salyers said local fish populations typically return pretty quickly.

“Basically the whole process will start undoing itself. The conditions that create the scenario of low oxygen will start slacking off, and as your temperatures cool down, the water will hold more oxygen,” Salyers said. “And as far as the fish recruitment back in the area, it’s amazing how fast they’ll come back. Next fall, it may be fantastic fishing in the Whiskey Bay area because you’ve suddenly reduced the competition so tremendously that now the bass and sac-a-lait that come in there have plenty of area to spawn. 

“They don’t have to compete like they’ve always had to. In those areas, it can literally be the difference of a single year and the fishing should rebound.”