Harsh South Dakota winters can take their toll on people, livestock, roads and just about everything else in the state.

That includes game fish in the lakes around the state, and the winter of 2018-19 proved no exception, as South Dakota Game, Fish and Parks Department recently completed its yearly procedure of testing lakes and restocking walleye, perch and other fish that died from the cold conditions over the winter.

The winter began fairly mild, but it turned cold and long, resulting in winterkill at a handful of regional lakes.

“This (winter) was one of the more severe years in awhile,” said Todd St. Sauver, area fisheries supervisor for South Dakota Game, Fish and Parks in Sioux Falls. “The winter started out pretty mild and we didn’t think anything would be a problem, but it turned severe in a hurry and lasted forever.”

St. Sauver said the GF&P no longer relies as heavily on oxygen testing of lakes to help determine winterkill. Newer methods, such as the use of submersible cameras and reports from fisherman out on the lakes, have helped create a more accurate picture of where winterkill has occurred, he said.

“We don’t do regular oxygen testing anymore, as it’s pretty unreliable in detecting winterkill. But a lot of fishermen use cameras, and we did get some reports of them finding some dead fish on the bottom (of some lakes). So we did some testing with our cameras,” St. Sauver said.

He said GF&P detected the most serious area winterkill at a handful of lakes: Oakwood East and Oakwood West in Brookings County, Lake Preston in Kingsbury County and Lake Cavour in Beadle County. All of those lakes have been restocked for the season, St. Sauver said.

St. Sauver said while this season was bad for some lakes, considering the severity of the winter, it could have been much worse.

“All in all, I think things turned out better than we expected. We did not see as many severe winterkills as we were expecting. That was a good thing. All the lakes that did have severe winterkills have been restocked, and we normally see really fast fish growth,” St. Sauver said. “Hopefully, those waters will be up and providing some fishing again in two or three years.”

GF&P begins looking for winterkill in the spring and then conducts a yearly summer survey to determine which lakes are hardest hit.

“That is pretty much our standard operating procedure. Every spring, whether it’s a severe winter or not, we look for dead fish and when we find them we do some spring testing. That gives us a rough idea on what happened and if we need to restock right away,” St. Sauver said. “And every summer we do our fish population survey, and in the case of partial winterkill, that will give us additional information.”

When dealing with winterkill, St. Sauver said the GF&P generally restocks lakes with walleye and perch, as they are two of the most popular game fish prized by South Dakota anglers. They also are species that tend to be affected most by cold winter conditions, unlike northern pike, he said.

“We primarily restock perch and walleye because it’s what we have most available to us. We’ve learned over the years that northern pike really don’t need to be restocked, especially in high water years. They spawn on their own and are winterkill-resistant,” St. Sauver said.

It can take time for restocked lakes to recover from severe winterkill, St. Sauver said. And in addition to inconveniencing anglers, it can also cause problems for the GF&P. Lake Preston, for example, is a lake where fish are usually removed to restock other lakes in the state. When winterkill hits it, it can affect how easy it is for the GF&P to address the issue at other lakes.

“Lake Preston had severe winterkill,” St. Sauver said. “But it doesn’t provide much angling. It does provide some utility for us, though, in taking adult perch out to restock other lakes.”

While the GF&P works to minimize the impact of winterkill, there can also be a positive side to the phenomenon, St. Sauver said. Undesirable fish also die off during harsh winters, allowing restocked game fish to thrive without competition.

“Winterkill is not all bad. In the case of the Oakwood lakes, thousands of carp were killed. Sometimes you get a better lake quicker when you set the rough fish population back a little bit,” St. Sauver.

St. Sauver said the GF&P method for dealing with winterkill has evolved over the years, but the best way to address the issue is locating where the worst damage has occurred and addressing it through restocking. Winterkill is likely going to occur no matter what happens, he said.

“Aeration in shallow lakes is basically ineffective. That’s been done for a long time, and it’s still done in a few areas, but you won’t find many state agencies that want to pay for it,” St. Sauver said. “It’s much less expensive to restock.”

Unless there are changes in the way the public wants to deal with the issue, the GF&P will continue to monitor and restock lakes as necessary, he said.

“The only real answer for a lot of these lakes is making them deeper, and that’s not going to happen until society decides to spend millions of dollars on lakes,” St. Sauver said. “It’s just the nature of the beast with our lakes. A lot of them are shallow, and a lot of whether or not they produce good fishing depends on our stocking program and how many a year can survive.”

Until then, St. Sauver said, winterkill severity will be determined by how harsh South Dakota winters get.

“Mother Nature is a huge variable that we have no control over. She can thwart our best efforts at will, pretty much,” St. Sauver said.