PIERRE — Many in the community have noticed a number of dead, floating fish in Lake Sharpe but officials with South Dakota Game, Fish and Parks said it’s a sign of high times on Lake Oahe and nothing to worry about.

Two weeks ago, Game, Fish and Parks began receiving reports of dead fish in Lake Sharpe. John Lott, chief of aquatic resources for Game, Fish and Parks, said most of the fish are lake herrings that were entrained, or transported through the dam with the flow of water. He said it’s unknown how many fish have been killed so far or what that number is likely to be this summer. He said the trend is likely due to the increased water level of Lake Oahe and a larger area of cold water than in past years, which herring prefer.

“Our best guess is there is just a good bunch of lake herring in the lower end of the reservoir and as a result we’re seeing those in the tailraces mortalities,” Lott said of fish in the area of water where water enters the Missouri River.

Courtesy photo Justing Holthus, of Game, Fish and Parks, holds lake herring near the Oahe Dam. This year anglers and boaters are noticing an increase in the number of herring washed up along the river banks, which is likely due to higher water levels and more cold water, official say. Advertisement

Chris Hull, with Game, Fish and Parks, said Lake Oahe is considered a two-story lake, with an upper warm water layer and a lower cold water layer. Herring, as well as rainbow smelt and Chinook salmon, prefer cold water. In recent years of drought, the cold water zone was smaller and fish in those areas were safely below intakes in the reservoir. Now, because there is more water, the cold zone has grown and herring, for example, are closer to places where the water is pulled to go into Lake Sharpe.

Lott said the number of herring killed might indicate a large number of herring in Lake Oahe or they might be fish that are too large for walleye and pike and other predator fish to consume and become excess. Lott said the kill is a concern but less serious than other types of kills — contaminations or fish diseases.

“We’re certainly monitoring it,” he said. “This is just a part of the normal operating procedures of Oahe Dam.”

Lake Herring were introduced to Lake Oahe by Game, Fish and Parks in the late 1980s and early 1990s. Lott said they were intended to be an additional cold water fish capable of growing larger than smelt and maintaining a more stable fish population. He said more lake herring or smelt in Lake Sharpe because of more water in Lake Oahe can mean a better fishery and more fish anglers like, such as walleye.

“Those walleyes like that colder water,” said Lott, “If they know there will be smelt coming through they stay right by the tailrace, and when the water starts to come through in the evening they’ll start to feed on the smelt that pass.”

Lake herring are larger than smelt, which are considered big at eight inches long and one inch in diameter. Lott said lake herrings might have difficulty passing through the dam because of the pressure change or body size.

“It’s just some of them have issues with the pressure or the temperature or they’re physically injured,” he said. “It’s a heck of a change in pressure from being 78 to 88 feet deep right now to being on the surface.”

Some of the dead fish will be consumed by catfish or other fish and Lott said the high level of water in Lake Oahe can benefit Lake Sharpe without hurting the fishery in the reservoir. 

“Whenever you build a dam, you stop the natural downstream movement of nutrients and fish and food,” he said. “This is one way we’re still able to get some of those nutrients and food moving downstream. There are times of course when a loss of fish out of a lake through entrainment is a cause of concern.”

Lake Oahe was at a depth of 1,612 feet Monday. A year ago it was at 1,594. However, in 2006 and 2004, it was down to about 74 feet.