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Large fish kill found on Missouri River; cause unknown but thought natural

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outdoors Mitchell,South Dakota 57301
The Daily Republic
Large fish kill found on Missouri River; cause unknown but thought natural
Mitchell South Dakota 120 South Lawler 57301

CHAMBERLAIN -- Hundreds of fish were reported dead recently on the Missouri River's Lake Francis Case, but authorities say the cause was probably natural.


State Game, Fish and Parks officials were made aware Friday of a large fish kill in the White River confluence area, said Geno Adams, senior fisheries biologist with the GF&P. Some of the reports came in Thursday from anglers to Cedar Shore Resort, in Oacoma, and the official reports came the next day to the GF&P, Adams said.

The cause of the fish kill is currently unknown, Adams said, but the general consensus among biologists and GF&P staff is that there may have been a low water level in an area of the river.

A section might have pooled and gotten cut off from the rest of the river, which decreased the oxygen and killed the fish. Then a drastic increase of water later in the week could have flushed the fish out.

"It's a natural occurrence when you get low oxygen levels," Adams said. "The deterioration of the fish and the stage they were in is why we think (the fish died) earlier in the week."

Cedar Shore Resort marina worker Miles Clark, of Oacoma, was one of those who reported the dead fish on Friday.

"The only thing that I heard was that there were fish floating down there and I called the Game and Fish. I had a couple different people stop and tell me about it," Clark said.

Anglers also called the GF&P on Friday.

"The anglers that aren't used to seeing dead fish, or dead fish in various stages of decay, were calling in different fish that weren't actually dead, which is why we sent a biologist to see what he thinks," Adams said.

The majority of the fish were river carp suckers, channel catfish and paddlefish. There also may have been a few buffalo or redhorse fish. Some of the fish were too decomposed for positive identification.

The biologist who investigated, Jason Sorensen, reported about 60 paddlefish and hundreds of catfish and carp suckers.

"On a 100-yard stretch," Adams said, "you might find 30 to 40 fish."

Sorensen reported the majority were at the mouth of the White River down to the Elm Creek area.

In a related matter, Adams said in a press release that individuals who had been on Lake Francis Case or near the White River earlier in the week reported seeing fish "exhibiting unusual behaviors."

Adams said that toxic substances or chemicals could always be a possibility, but he said the area is not surrounded by a large amount of agricultural land and this is not the right time of year for farmers to use chemicals on fields.

The fish will not be tested for toxicity levels because it is impossible after they are dead, he said. "(The fish) must be on the verge of death -- in the stage of decay they were in, there was just no way you're going to get anything back (from the tests)."

Other ways large fish kills can occur include high water temperatures or bacterial and viral infections.

"What I'd like to try to stress to people is that these fish kills that occur naturally in reservoirs (and other isolated areas) ... generally aren't going to impact the aquatic system in the area," Adams added.