WORTHINGTON — Hundreds of decaying carp, bullheads and walleyes are washing up along the shore of Lake Ocheda’s west basin as the ice cover begins to slowly melt away and reveal the impact sustained low oxygen levels have had on this shallow prairie lake.
The dead fish are an indication of just how bad it became for aquatic life, with low water levels going into winter and the deep chill that froze portions of Lake Ocheda all the way to the its bottom.
Ryan Doorenbos, Minnesota Department of Natural Resources Fisheries Supervisor at Windom, said 17 southwest Minnesota lakes have been on the watch list since low levels of dissolved oxygen were found during readings taken throughout the winter. The number of lakes being watched is double this year compared to the average.
“We’ve been in a drought scenario the last two to three years, and we went into winter a foot or two feet lower than normal (for lake levels),” said Doorenbos. “Combine that with the ice thickness; and some lakes went into winter green (with algae) — that sucked some oxygen out of the water.”
When the dissolved oxygen level gets below 2 parts per million, it’s cause for concern. The west basin of Lake Ocheda registered .1 ppm at its worst. The Nobles County lake south of Worthington wasn’t the only area lake with such a low reading. The same reading was taken on Kinbrae Lake in northern Nobles County and Bingham Lake in Cottonwood County.
Popular fishing lakes like Little Spirit in Jackson County had dissolved oxygen levels as low as .8, Nobles County’s East Graham hit a low of .6 and West Graham was down to .4 toward the end of winter. In Murray County, North Fulda Lake recorded a low of .2 ppm, and Lake Louisa was down to .3.
“Louisa is the one we fully expect to see dead fish on,” said Doorenbos. “It was low right away and continued to stay low.”
Dead carp have been found on North Wilson Lake near Lake Wilson in Murray County; and Talcot Lake may have losses after recording a dissolved oxygen level of .6 ppm.
Doorenbos said the DNR gets concerned when the dissolved oxygen level gets down to 2 ppm because they anticipate seeing stressed fish.
“It may not necessarily mean they’re dying,” he said, adding that the duration of low oxygen levels plays the greatest role in fish survival.
With 17 lakes on the watch list in southwest Minnesota, the spring thaw on area lakes may reveal some of the biggest fish kills in recent years on some lakes.
“It’s a natural process for these pothole prairie lakes that are shallow and fairly nutrient rich,” Doorenbos said. “There are management things we can do that can quickly rebound a system.”
“We experience winter kills each winter, but it’s those severe ones where you see several thousands of dead fish (that are less frequent),” he added.
Cedar Lake in Martin County, near Trimont, has suffered “significant” winter kill, revealed when ice came off that lake a couple of weeks ago.
The DNR takes dissolved oxygen readings on area lakes throughout the winter months as a way to measure how aquatic life is doing.
“From a planning standpoint, we take dissolved oxygen readings for stocking,” Doorenbos explained. “The telltale sign is when the ices goes off — how many dead fish are we seeing?”
Based on the low readings recorded this past winter, and the amount of dead fish being discovered on the shorelines this spring, big losses of game fish are a concern for the DNR.
“Some of these basins we have used for brood source lakes in the past, where we have good populations of crappies or perch,” Doorenbos said. “We do have some concerns that the number of fish available might be difficult to find.”
The DNR will do sampling once the ice is off the area lakes to see what species have survived and compare those to what species were prevalent in previous samplings.
“That will trigger management and stocking,” Doorenbos said.
While extreme winter fish kills have a negative impact on the fishery, there are some positives that can come from the natural disaster. For instance, Doorenbos said Lake Louisa, because of its anticipated major losses this year, may be used as a walleye rearing pond.
“Generally these walleye fry do really well,” he said. “Usually, growths in lakes following a winter kill are just awesome.”
Once the DNR identifies stocking needs on area lakes, Doorenbos said any fish moved from one lake to another will have to be disease tested.
“Our goal is to get these fish into basins pre-spawn, so when they get to the winter kill lake, they will spawn in the lake and create a quick rebound of the lake,” he added.
Doorenbos is asking for the public’s help in identifying lakes with winter fish kills.
“If you’re out and about and see dead fish, make a mental note of what species you see and also the numbers,” he said. “Even if you see 50 dead fish, that’s at least noteworthy for us to hear about from a management standpoint.”
To report winter fish kills, contact Doorenbos at (507)-831-2900, ext 232, and leave a message with the name of the lake, an estimated number of dead fish and the species seen.
To view a complete list of area lakes and the dissolved oxygen readings recorded, visit http://files.dnr.state.mn.us/areas/fisheries/windom/lakes/winteroxygen_2....
Daily Globe Reporter Julie Buntjer may be reached at 376-7330.