WORTHINGTON — Pulling a plastic sled that contained an ice auger and equipment to measure dissolved oxygen, Okabena-Ocheda Watershed District Administrator Dan Livdahl trudged across a frozen Lake Ocheda Wednesday afternoon to take his weekly measurements of dissolved oxygen, ice thickness and water depth.
The measurements have produced a bit of a mystery.
With 13-inch-thick ice covering 10 inches of lake water, dissolved oxygen on the lake’s west basin still measures more than 22 milligrams per liter (mg/L) — far higher than the 8 mg/L that is to be expected. This is the second consecutive winter the dissolved oxygen level in the lake has exceeded expectations. Last winter, tiles remained running, supplying a steady flow of water and oxygen to the lake. This winter, the tile aren’t running — and yet the oxygen level remains high.
The high levels are concerning because the watershed is in the midst of a drawdown on Lake Ocheda. It was able to get the lake’s water level down to two feet last fall, and needs a cold winter with enough ice to freeze out the fish.
Lake Ocheda is heavily infested with common carp. If it's successful in getting a massive fish kill, the Minnesota Department of Natural Resources would reintroduce a variety of gamefish to keep the carp population under control in the three-basin lake.
Livdahl had been on the lake’s east basin on Tuesday. There, he found 13 to 15 inches of ice atop 18 inches of water.
“The dissolved oxygen is a little lower than what it was a month ago,” he said, noting that the 14 mg/L was still pretty high. “We need some cold weather and hopefully we can make some progress here.”
Lake Okabena seining
Southwest Minnesota’s commercial fisherman was expected to be in Worthington this week to conduct a seining effort on Lake Okabena to capture and remove invasive carp. However, an East Coast blizzard earlier in the week slowed the return of his fish-hauling trucks.
Plans are now tentatively in place for Scott DesLaurier to be in Worthington sometime next week, according to Livdahl, who reported the information to the watershed’s board of managers in a Tuesday afternoon meeting.
Livdahl said there are still some concerns with the plan for seining next week. He’s been tracking the 15 carp surgically implanted with radio frequency tags, and while the carp had congregated in two groups southwest of Centennial Park last week, oxygen levels in the water are far higher than DesLaurier would like.
At the current dissolved oxygen level of 8 mg/L, the carp remain quite active and will likely swim outside the area where the seining will take place, Livdahl said. Lower oxygen levels — closer to 4 mg/L — would keep the roughfish in more of a sedentary state, he added.
When the seining is conducted, Livdahl said any of the tagged carp — the 15 with radio frequency tags and the 200 that were fitted with Passive Integrated Transponder (PIT) tags in October 2019 — that are captured will hopefully provide engineers with Wenck the numbers needed to better estimate carp population in the Worthington lake.
Several volunteers have offered to assist with the seining operation.
In other action, the board:
Agreed to schedule a meeting with Houston Engineering and ISD 518’s operations committee to further discuss potential water quality projects on the school district’s property along Crailsheim Road.
The site has the potential to treat runoff, thereby improving water quality before it reaches Lake Okabena. The site could also be used to reduce downstream flooding risks.
Houston Engineering has developed several preliminary concepts for water quality Best Management Practices on the school district’s property, which it wishes to present to watershed and school district board members. Together, the hope is it could determine projects for the property, which Houston Engineering would then design, model and evaluate success in meeting water quality goals. Cost and load reduction estimates would also be developed.
“I feel like the school district property could make the biggest difference for Lake Okabena in long-term water quality,” said Manager Jay Milbrandt.
Reviewed the 2020 annual report, which recaps some of the progress made on projects within the watershed district throughout the year.
Discussed, but took no action, on a draft of the 2021 annual plan. The plan outlines projects the watershed district plans to work on this year.
“A lot of the projects are a continuation from 2020,” noted Livdahl, including efforts at Prairie View, the trio of lakes — Okabena, Ocheda and Bella — and the potential collaboration with ISD 518 on the school district’s property along Crailsheim Road.
Authorized the hiring of Dennis Rick Limited, Worthington, to conduct the watershed district’s annual audit at a cost of $3,900.