SIOUX FALLS, S.D. (KELO)– On Wednesday, we showed you the fish kill at the Lake Vermillion spillway, which was caused by heat and lower water levels. Fish kills are typical each year in South Dakota, said Dave Lucchesi, Area Fisheries Supervisor, and they often happen in late summer.
Factors that play a role in fish kills include warm water and low water levels, Lucchesi said. Low oxygen in the water happens because at night, plants stop photosynthesizing and they need to consume oxygen, so then there is very low oxygen in the water.
“Fish need the oxygen to breathe, and if that period lasts long enough, we have some fish dying,” he said.
The fish kill at Lake Vermillion was a large number of fish, Lucchesi said.
“What happened there is fish congregate up at that dam or spillway and what happened there was that the flow, the water stopped flowing with the low water and they were in that, trapped in that pool, and when you had that happening with the low oxygen at night, those fish were suffocated basically and that’s why you had such large number,” he said.
Lucchesi does not think that algae played a role in the Lake Vermillion fish kill.
It looked like most of the fish were common carp, Asian carp and gar, which are commonly found in South Dakota rivers, Lucchesi said.
Ideal water temperatures during the summer are between 70 to 75 degrees, Lucchesi said. But, he believes that lake temperatures have exceeded 80 degrees in some of the lakes in the state on these hot days, which is fairly warm for South Dakota.
‘I would expect to see temperatures decreasing with the current forecast and the day length is getting shorter and so longer periods of nighttime,” he said. “Typically, I think our maximum water temperatures are often achieved in July.”
With warmer water temperatures, you have less oxygen in the water, and the fish’s need for oxygen increases, he said. Fish become more stressed under those situations as well, and it played a role in the Lake Vermillion fish kill.
Often, when there is a fish kill, the Game, Fish and Parks department does not do fish cleanup, he said. Usually, those fish will decompose, but Lucchesi is not sure in this situation, with such a build-up of fish, whether or not any action will be taken. It is often the responsibility of the adjacent landowners at the area to remove the fish carcasses.
“But they do decompose pretty quickly in the summer sun,” he said.
We have gone through an interesting period, with record-high waters in 2019 and early 2020, and now very dry conditions and extremely low water levels, Lucchesi said.
“Often when we get low water and high temperatures, we start to see more of these fish kills occur,” he said.
This summer, the state has had around four fish kills reported, Lucchesi said, with most of them happening on marginal waters, which are shallow and they are typically carps or minnows.
They did see a particle fish kill on Lake Menno, where some blue gills and a few bass were reported dead, he said.
Fish kills are something that we can expect to see more of with the recent drought conditions, Lucchesi said.
“You’re going to expect more summer kill,” he said. “Also, if we were to have a severe winter after this, we might expect some more winter kill because there’s less water in the lakes and fish are more concentrated. So, if we have a severe winter following a drought situation, that often spells winter kill for our fish.”
Places that can expect to possibly see more fish kills are the marginal water areas, Lucchesi said. These include water bodies that are shallow, have higher productivity and higher quantities of aquatic vegetation.
“But you never know in these situations, sometimes deep waters that have stratified…if we get a cold snap here and the lake starts to turn over, we see fish kills with that,” he said.
There isn’t really anything they can do to prevent summer fish kills, Lucchesi said. They can’t try to remove fish or move fish from one spot to another.
“They’re just kind of a part of prairie lakes and we expect them when the conditions are as such,” he said.
In order to get the water levels back to normal and the spillways running again, it’s either going to take some late summer rains and quite a bit of precipitation, or it is going to take some snow this winter.
“We need the moisture and if we get a lot of snow, we should expect good spring run-off and the water will start to flow again,” he said.
After a drought, often water levels can return to normal pretty quickly, it just takes a fair bit of snow or rain over a short period of time, Lucchesi said.