Oxygen levels looking good
SLAYTON -- Word from Murray County Parks Director Justin Hoffman to commissioners last week was that Lake Louisa's oxygen level was low, something the Minnesota Department of Natural Resources (DNR) is keeping an eye on.
"We (take readings) to inform the commissioners and local anglers," Hoffman explained. "The DNR does testing too, and does a better job of recording their findings."
Hoffman said the only problem lake so far is Louisa, a small prairie pothole located southwest of Westbrook. Late in the week, Hoffman said the DNR had gotten a reading of 0.3 percent, while Hoffman had a reading of 0.9 percent approximately 100 yards off the landing.
"It can depend on where you're taking the readings from," he said.
DNR Fisheries Technician Chuck Obler said he takes a second reading in another spot when he gets a low reading.
"I got a 0.3 by the access on Louisa, and less than 2 percent can cause stress or fish kills," he stated. "Over by the aeration system it was OK, 2.1 percent. Fish can still be alive, just not real active."
Obler isn't surprised to see Louisa showing low oxygen numbers, nor is he surprised to see Lake Corabelle showing the same symptoms.
"Both are lakes that are five and a half feet deep," he explained. "They typically go low every winter."
Obler had recently finished taking oxygen readings at lakes in Lyon, Lincoln and Murray Counties and said most of them ranged from 7 to 15 percent oxygen.
"I do 35 lakes in the area, and for this time of year and the amount of snow we have, things are looking very good. Sarah was at 16.6, Shetek's north side was at 9.6 and the south side was at 9.2."
The readings were taken before southwest Minnesota got drenched in showers of rain, followed by inches of snow, which may well affect the next readings.
"Things can change in a hurry," Obler said.
The oxygen level in a lake are influenced greatly by light penetration, and when snow cover gets 4 to 5 inches deep, oxygen goes down. When that happens, there isn't much that can be done.
"The only thing I've seen somewhat work is on a smaller lake system - they have been able to stabilize by plowing or blowing snow off a lake," Obler stated. "Once that level starts dropping and its low, there's not much you can do. Even more aerators won't help." Obler said.
Many area lakes, Louisa included, have an aeration system that keeps a portion of the lake from icing over, allowing oxygen to enter the water. But, as Obler explained, the aerator does not pump or force oxygen into the water, and when it pulls warmer water from the bottom of the lake to the top to keep the ice away, it also churns the oxygen-rich top waters down to the bottom.
"The best oxygen is always right under the ice, and the fish will move up to the ice with the oxygen," Obler said. "The aerators can sometimes do more harm than good. We can actually kill fish by aerating water."
Last winter, there was a substantial winter kill on Lake Shetek, but according to a DNR report, the effect on game fish populations such as walleye, perch and crappie were minimal.
"The kill on Shetek was mostly carp and buffalo," Obler said. "There has been fabulous walleye fishing all fall, summer and winter, and the walleye numbers in the lake went up."
Obler said bigger fish require more oxygen, which means when oxygen levels are low, an eight pound walleye is going to die before an eight inch walleye dies. Many of the fish also concentrated by the better oxygen in the lake, he explained, and basically used it up faster.
"There were 100,000 pounds of fish in one area," he stated. "The ones that stayed away from that area fared better."
Sometimes it is just a matter of Mother Nature taking her own course, no matter how much humans want to be involved.
"A few years back, Louisa went gangbusters for perch," Obler said.
Word got out that the bite was hot, and the tiny lake was covered with fishermen and women. Portable fish houses were wall to wall, and, if fish tales can be believed, the perch couldn't even resist a bare hook dropped down a hole in the ice.
"Typical of these shallow prairie lakes, you get a boom and a bust," Obler said. "With lakes like Corabelle and Louisa, there's a little bit of concern, but they are lakes that typically go low (oxygen) every year. I call them 'tweener' lakes. They're between a lake and a slough."
All Obler and the anglers can do is wait and see how the lakes will ride out the winter. In the meantime, Obler and another technician from the DNR will continue to monitor the oxygen levels of 65 lakes, collecting data every two weeks and documenting the information.