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Evidence of fish winterkill on Pocasse not alarming to GF&P

Reports of dead fish on Lake Pocasse have raised some concerns about winterkill on area lakes and ponds because of the heavy snow cover, but that might not be the case.
According to Dan Jost of the South Dakota Department of Game Fish and Parks Mobridge office, the dead fish might not be a product of regular winterkill.
There are several reasons winterkill occurs, and the fish found in Pocasse might have died for another reason, according to Jost. He visited the lake on Tuesday, March 26, and said there were several different species of fish, but not very many carcasses.
Winterkill is the loss of fish in winter because oxygen was lacking in a body of water. In small, shallow lakes the available oxygen can quickly be used up by live plants that consume oxygen in the evening, fish, and by bacteria that feed on dead and decaying vegetation. If there is a prolonged thick cover of ice or a heavy blanket of snow, sunlight is blocked, and vegetation can die.
“Every year we have some winterkill in the smaller lakes and dams,” he said. “Shallow lakes are very prone to it.”
Jost said because of the mild beginning to winter in this area, there was not a prolonged period when a thick coat of ice covered the lakes and dams. He said because of the location of the fish on Pocasse, by the Highway 10 Bridge that separates the east and west portions of the lake, moving water might be the culprit. He said the water being churned up in the area where the fish were found, could have caused a murky situation that caused the vegetation kill off, thus the fish kill.
“It is the only place so far that we have seen dead fish,” Jost said. “We have had fish kill in that area before but these could have been come from other areas of the lake and gathered right there.”
He said the GF&P staff will monitor the situation, but he is not really concerned about it.
“There is extreme minimal concern of fish kill in Lake Oahe,” said Jost.
He explained there are many factors, including the size of the body of water, the current and movement of the water, and depth of the lake, that keep winterkill from occurring.
Jost and other GF&P staff will be checking area lakes and dams for winterkill in the comings weeks. He asks residents that see signs of winterkill on lakes and dams to call the Mobridge GF&P office at 845-7814.
– Katie Zerr –