ORTONVILLE, Minn. — “Thousands to tens of thousands” of fish in Big Stone Lake died recently, but Minnesota Department of Natural Resources area fisheries manager Chris Domeier says anglers probably won’t notice.
The die-off happened a little over a week ago at the southern tip of the 27-mile long Minnesota-South Dakota border water near the city of Ortonville, about 2 1/2 hours south of Moorhead. Domeier said the fish-kill was likely triggered by a “perfect storm” of extremely warm weather, a massive algae bloom and a wind that blew the algae into the south end of the lake.
“Usually when these things happen, they are in localized bay areas and that’s what happened here,” Domeier said on 970 WDAY radio show Monday morning. “The algae, when it dies, decomposes and overnight the bacteria that’s decomposing the algae essentially use up all the oxygen in the water. If you’re a fish in the area this is happening, there’s a high probability you’re going to die just from lack of oxygen.”
Domeier says fish-kills in the Ortonville area, and even on Big Stone Lake, happen almost every year because the lakes in the area are often shallow, nutrient-rich prairie lakes that are susceptible to algae blooms. The advent of social media spreads the word about fish-kills faster, so people share photos and talk about them more.
The biologist did say, however, that this kill is “the most serious I’ve seen.”
“I’ve been here since 1991 and usually a hundred or two fish in a small area are killed,” Domeier said. “This one must’ve been a perfect storm. … There were thousands to tens of thousands of fish that died.”
The dead fish were mostly small perch, it appeared, but Domeier said few species were spared. Walleye, bluegill, largemouth bass, carp, suckers and even bullheads were floating in the lake. Most of the fish were small, 5 inches or less, but there were some impressive bass and walleye that died.
Domeier said for bullheads to die, the lack of oxygen must’ve been pronounced because the whiskered fish need very little to survive. Most fish need 2 parts per million and DNR staff measured oxygen in the water at 1 part per million in the affected area the day after the die-off.
“That tells me that overnight the oxygen levels might’ve been zero,” Domeier said.
Despite the thousands of dead fish, which decomposed or were eaten by birds in a couple of days, Domeier said angling shouldn’t be affected on the popular walleye and perch lake. Because of the lake’s size, the area affected is small and Big Stone supports a healthy population of fish.
“If I had to put a number on the percent of the lake’s perch population that was affected, I’d say one to three percent,” Domeier said. “It’s not going to be a significant number where you’re going to notice it when you go fishing in the future. We don’t like to lose any fish, of course, but this really shouldn’t affect anything.”