Lake Okabena's carp population may be substantially less than previous study estimated
No sign of zebra mussels on city-owned docks and boat lifts, but curly leaf pondweed was discovered in Lake Okabena earlier this year.
WORTHINGTON — Lake Okabena’s common carp population may not be as high as previously thought, according to new data received by the Okabena-Ocheda Watershed District.
The OOWD hired a Twin Cities-based company earlier this year to conduct a second carp assessment on the lake, this time using box nets to capture and dispose of the roughfish — and a formula to estimate how many more carp may be in the Worthington lake.
Lake Okabena has been on the state’s impaired waters list for the last decade for both water clarity and water quality. It was long believed carp were stirring up sediment in the lake and destroying submergent vegetation, leading to murky waters.
“People think they’re seeing a lot of carp in the lake,” OOWD Administrator Dan Livdahl said following the organization’s monthly meeting earlier this week. “What they’re seeing are buffalo (fish). Bigmouth buffalo are not as skittish …. Unless you know what you’re looking for, how do you know?”
Bigmouth buffalo look very similar to common carp, the primary difference being in the angle of their mouth.
Livdahl said while the district continues to await official results from the latest carp population study, preliminary data shows carp density in Worthington’s lake to be considerably lower than the previous study indicated.
In fact, the estimated carp population is now below the level at which carp are known to degrade water quality. Current data shows estimated carp density to be 68 pounds per acre — 21 pounds per acre below the 89-pound-per-acre density known to impact water quality — and about half the population density the watershed district was previously given as an estimate.
“That brings up an interesting conundrum,” Livdahl said. “Do you put effort in now to try to stabilize that level?”
It’s a lot less effort to maintain the existing carp population than to let the population grow and try to catch up in the future, he added.
And that is what the watershed board will have to decide. Through carp tracking in recent years, the board knows carp are congregating in Sunset Bay during spawning. It now faces a decision on whether to install barriers to keep carp from traveling between Lake Okabena and the bay.
Livdahl said that’s a discussion he and board members want to have with the Clean Water Partnership Joint Powers Board, which includes representation from the city of Worthington and a stakeholder who lives on the lake.
The joint powers board will likely meet in December, Livdahl said.
In other business, Livdahl reported to the board that he checked city-owned docks and boat lifts for zebra mussels after they were removed from Lake Okabena this fall. Thus far, he has not found any of the invasive species — good news considering zebra mussels were just reported earlier this week in Lake Shetek in Murray County.
“The bad news is this year we did get curly leaf pondweed for the first time,” Livdahl said.
The presence of curly leaf pondweed in Lake Okabena is the direct result of people not thoroughly cleaning their boats or watercraft before moving them from one lake to another.
It’s the exact behavior that could introduce zebra mussels to the Worthington lake.
While Livdahl checked city-owned equipment, he encourages lake property owners with docks and boat lifts to check their equipment for zebra mussels.
Anyone who finds something they believe to be zebra mussels on their equipment can call the watershed district to report it. It is mandatory to report the discovery to the state.