Lake Ocheda drawdown could happen next fall
WORTHINGTON — The Okabena-Ocheda Watershed District and Minnesota Department of Natural Resources hosted the last of three public informational meetings Monday on a management plan for Lake Ocheda.
Plans are to improve water quality in the nearly 18,000-acre, three-basin shallow prairie lake through periodic drawdowns, reducing the roughfish population and encouraging submergent vegetative growth. A plan written by the DNR, with watershed and public input, will need to be approved before a drawdown can begin.
The plan will be presented at a public hearing Oct. 10 in Worthington, with Dennis Frederickson, DNR Southern Region Director, serving as the hearing officer. The meeting time has yet to be finalized. Frederickson will gather oral and written testimony and present all of the materials to the DNR commissioner, with a final ruling on the plan anticipated in three to six months.
If the plan is approved, Okabena-Ocheda Watershed District Administrator Dan Livdahl said a drawdown would realistically begin in August 2019. It could happen in the fall of 2018 if authorization and permits are granted quickly.Impaired water
Lake Ocheda’s west basin was added to Minnesota’s Impaired Waters list in 2010 for high nutrient levels, while the Ocheyedan River, which stretches from Lake Ocheda to Lake Bella, was listed as impaired in 2014 for high levels of sediment.
The water from the lake and river flow into Worthington’s wellfield at Lake Bella and supply drinking water to the city of Worthington.
Livdahl described Lake Ocheda’s waters as brown, high in nutrients and laden with roughfish. DNR estimates from several years ago put the lake’s carp population in excess of 600 pounds per acre. Water clarity is at eight inches or less and phosphorus levels are at 248 parts per billion, compared to 90 parts per billion in a healthy lake.
“To get Lake Ocheda off the impaired waters list, we need to reduce 95 percent of the nutrients on the bottom of the lake that get stirred up,” Livdahl told attendees at Monday’s meeting. Removing roughfish and encouraging vegetative growth are the top two priorities to improve water clarity.The plan
The watershed district began meeting with riparian landowners in September 2009 regarding a possible drawdown of Lake Ocheda. It wasn’t until May 2015 that the OOWD asked the DNR to help write a management plan for the lake.
The plan includes a gravity-driven lake drawdown to take water depths to two feet, with reliance on Mother Nature for a full freeze-out.
“If we can restore some submergent aquatic plants out there, get a good fish kill and get in some new (predator) fish, that drawdown could last five to 15 years,” said Josh Kavanagh, DNR Wildlife Lake Specialist. He said water levels should rebound by late June, following a fall drawdown.
Future drawdowns would be determined by a project management team that includes representatives of the watershed district, the DNR and community members.
The ultimate goals of the project are to achieve water clarity of 2.3 feet or greater through secchi disk readings, 65 percent coverage of aquatic vegetation on the entire lake and reduced phosphorous levels.
In 1961, more than 60 percent of the lake had aquatic vegetation, according to DNR records presented by Area Wildlife Supervisor Bill Schuna. By 2005, it was down to 20 percent, and since 2011, no aquatic vegetation is present.
“A healthy shallow lake should have vegetation,” Kavanagh said.Getting to work
An estimated $300,000 in improvements are needed on the 1941-era dam on the south end of the west basin prior to the first drawdown. The work will include replacement of existing wooden stop logs and the addition of a fish barrier to include a headknocker to prevent carp from entering the lake through the Ocheyedan River, as well as a vertical screen for use during high water flows to keep the roughfish out.
Livdahl plans to apply for grants for dam improvements, although the watershed district has set aside a portion of its annual levy for the work.
Questions from attendees Monday ranged from water quality coming from farmland tile and surface waterways — both considered sources of phosphorus reaching the lake — to using chemical treatment to kill roughfish if a drawdown isn’t successful and concerns a drawdown would have for private well owners.
Chemical treatments such as Rotenone are expensive and are a concern because of the city’s wellfield, explained Livdahl, while Kavanagh said private well levels should not be impacted by the drawdown.
“If Lake Ocheda is successful (the vegetation on Fulda Lake) is what you can expect to see,” Livdahl added. “That is the kind of vegetation we’re looking for, and that is the vegetation that clears up the water quality.”