Note: This story has been updated with Game Fish and Parks confirmation of a winter kill in Huron.

SIOUX FALLS, S.D. (KELO) — Lake and river levels were likely low at the start of December across South Dakota. So now that heavy snow and ice arrived in December and early January, what can happen to the fish in these conditions?

Winter kill is a threat.  Winter kill is the loss of fish in winter because oxygen was lacking in the waterbody, according to the Minnesota Department of Natural Resources. During the winter snowpack and ice can block the sunlight which harms plants and fish. Plants produce less oxygen which harms, and even kills, fish.

“One of the big issues we really have this winter is that in most of eastern South Dakota, we had a really dry summer and fall,” said Dan Loveland of South Dakota Lakes and Streams Association. “Most water bodies went into the winter with very low water levels.”

Subzero temperatures froze water bodies and heavy snow covers that ice. “We have much more snow cover,” Loveland said.

The combination can lead to winter fish kill as snow and ice block the sunlight. The lack of sun harms plants and fish.

Tom Landmark is a member of the Lake Hendricks Improvement Association in Hendricks, Minnesota. The lake covers about 1,500 acres in Minnesota and South Dakota.

The association has placed an aeration system in the lake for at least 20 years, Landmark said.

The Minnesota DNR has a Lake Aeration Program. According to the program’s website page, “aeration systems agitate and mix water in the lake. Warmer water near the bottom of the lake rises to the surface and melts an area of the ice.” The aeration system raised the oxygen levels in the lake.

“Statistics say that aeration may raise the oxygen level by a few percentage points,” Landmark said. But in a winter like this one with heavy snow and ice, a few percentage points can be especially important, he said.

The water levels in Lake Hendricks at its deepest are about 10 to 11 feet which is about 1 foot to 1 1/2 feet below normal, Landmark said.

The South Dakota Game Fish and Parks confirmed on Jan. 24 that there was sizeable winter kill at Huron’s 3rd Street rapids.

“Shortnose and longnose gar and silver and bighead carp comprise a large portion of this winter kill,” GFP communications director Nick Harrington said in an email to KELOLAND News. “GFP continues to have staff on site to monitor the situation.”

Shallow lakes and rivers can be the most vulnerable to winter kill.

Dave Bartel, manager of the James River Water Development District, said the pooling of fish near the dam and any fish deaths were not caused by the dam construction project. “I don’t believe the dam at 3rd Street had anything to do with (fish kill),” Bartel said.

The James River, like many lakes in the state, has a low water level with snowpack. That is “eliminating a lot of oxygen in the river,” Bartel said. Fish were forced to open water by the dam, he said.

Often, evidence of winter kill will be seen in the spring after ice and snow melt from the lake and dead fish pile up.

The Federal Bureau of Reclamation oversees the James Diversion Dam and Reservoir are located on the James River about 17 miles north of Huron.  Sterling Rech of the Billings, Montana, office said there were no actions on this diversion dam or reservoir that would have impacted fish or flows in the area of Huron and the 3rd Street dam.

“GFP fisheries staff monitor winter kill through the spring. Based on the severity and species lost, GFP will make stocking recommendations for impacted waterbodies as deemed necessary,” Harrington said in his email.

Various Minnesota lakes have had success with aeration systems.

Tom Hovey of the MN DNR said he’s not a fisheries expert but he works with aeration permits.

“In a lot of cases, our fisheries say they think it works well,” Hovey said.

Landmark said the system in Lake Hendricks has been successful. He’s been a member of the improvement association for 15 years and he’s never seen a winter fish kill in the lake.

The agency requires a permit for the operation of an aeration system, said Hovey.

“It’s a permissive system. We don’t actively find lakes to place aeration systems,” Hovey said.

The DNR will review permits to determine if an aeration system will benefit the lake and fish, he said.

“One of my biggest concerns is safety because you are creating open water and thin ice,” Hovey said.

Landmark said permit holders are required to have signs on the lake and in the aeration area that warn and notify of thin ice and the aeration system.

Signs for an aeration system at a lake in Minnesota. Minnesota Department of Natural Resources photo.

He said there is at least about 100 signs around the Lake Hendricks system.

The DNR offers to waive the $250 permit if the application meets agency standards, Hovey said.

But the systems aren’t suitable for every lake in the state, Hovey said.

Minnesota has more than 10,000 lakes and some of those lakes are best suited for waterfowl production and use. An aeration system would not fit in that case, he said.

“In other cases, the state will not push them, even in southern Minnesota…,” Hovey said.

Southern Minnesota may have more shallow lakes than other parts of the state but some of those shallow lakes may be well connected with a supply of fish within a watershed district, he said. In the case of a winter kill, those lakes are able to repopulate and may be in better condition after a winter kill, he said.

Sportsman’s clubs, lake improvement associations, counties or even cities will apply for permit to operate an aeration system.

The MN DNR aeration map shows clusters of aeration systems around the state including Lake Hendricks and Lake Benton in southwestern Minnesota.

A Minnesota Department of Natural Resources map of aeration systems in the state.

Hovey said the DNR works with associations and others who apply and have received permits.

Landmark said the DNR told the Lake Hendricks group on Dec. 30 that it had recorded low levels of oxygen in several lakes. The DNR’s contact prompted the association to install its four aerators on Dec. 31 instead of about a week later, he said. The four aerators are located at the city’s lakeside park.

At least three lake associations contacted in eastern South Dakota said they do not have aeration systems on their lakes.

The Lake Cochrane association does not have an aeration system but it has active springs, said association co-president Susan Norgaard. The active springs may help keep oxygen levels up, she said.

Loveland said he and another representative recently attended a meeting of an association near Madison which asked GFP officials about aeration systems. The GFP said then it was reluctant to use the systems because they weren’t sure they were effective and because of the potential hazard with the open water. Loveland said the GFP said open water may not be seen by lake users, especially at night.

The MN DNR has a checklist for those who plan to install an aeration system that includes the need to properly post signs to inform of aeration systems on the lakes, as well as choosing the proper system.

Winter kill can benefit a lake that has a heavy non gamefish population, according to the MN DNR. The population of a species such as carp can be thinned in a winter kill, according to the DNR.