WORTHINGTON — It’s likely a total fish kill has occurred in the pool below the Lake Bella spillway south of Worthington as a result of low oxygen levels in the water.
Ryan Doorenbos, fisheries supervisor with the Minnesota Department of Natural Resources office in Windom, investigated a report of dead fish in the water body on Sunday — primarily to look for the presence of invasive carp, which have been found there before.
What he pulled from the mess of dead and decaying fish were half a dozen silver carp. He also noted the possible presence of bighead carp, though it was difficult to tell with fish still frozen in the ice.
“There’s probably another five to 10 out in the middle in the ice,” Doorenbos said Wednesday morning. “I could tell that they were carp — more than likely one of the two invasive species. You can’t tell when they’re curled up and frozen in the ice.”
After alerting the DNR’s Aquatic Invasive Species group to the discovery, Doorenbos said he doesn’t plan to conduct another search of the dead fish once the ice melts. He doesn’t anticipate doing any seining in the pool either, believing no fish survived the winter.
“It looks like it was a pretty massive winter kill,” he said. “It would surprise me if there is anything that survived.”
The Ocheyedan River south of the spillway dried up last summer, trapping fish in the pool. Okabena-Ocheda Watershed District Administrator Dan Livdahl noted a significant fish kill in mid-August.
Doorenbos said this latest discovery is likely due to more oxygen consumption during a period of less oxygen creation in the water.
“In the last year, with the lack of precip, the outlet was not flowing,” Doorenbos explained. “As a result, you have a high biological oxygen demand. You have a lot of fish consuming oxygen in the water, and as the winter goes along, you don’t have any creation (of oxygen), to the point where they succumb to death."
In both the August fish kill and the one noted now as the ice melts, it appears the vast majority of the fish that died were carp — the common and invasive varieties, as well as buffalo fish and bullheads.
That invasive carp were found in the pool wasn’t really a surprise.
“We know that it’s a spot where essentially (invasive carp) can access from the Little Sioux River in Iowa,” Doorenbos said. “It doesn’t matter that they get to that point because it’s a dead end road for them.”
The concrete spillway at the southern end of Lake Bella provides no way for the invasive species to get into the lake and move through the Okabena-Ocheda Watershed.
Of the six silver carp Doorenbos retrieved from the pool, four were males, one was female and one was too far decayed to identify. The female silver carp was the largest, at just over 26 inches in length, with the smallest measuring 22.5 inches. Doorenbos noted this was in the range of the invasive carp captured last year in the pool below the spillway.