Three Eastern Nebraska Lakes Experience Severe Die-Offs
LINCOLN, Neb. – Three popular eastern Nebraska lakes experienced severe winter die-offs, causing Nebraska Game and Parks Commission biologists to restock them and adjust management practices to help prevent future similar occurrences.
The lakes involved were Memphis Lake at Memphis State Recreation Area (SRA) in Saunders County, and Lakes Nos. 4 and 7/8 at Fremont Lakes SRA in Dodge County.
Mark Porath, a Commission biologist, explained what causes this type of die-off. “During an extended winter, abundant aquatic vegetation that dies off and begins to decay removes oxygen from the water column making the conditions tougher for fish to survive, especially larger bodied species that have higher oxygen needs. The more severe the depletion of oxygen, the smaller a fish has to be to survive,” he said.
“The amount of decaying matter and the production of new oxygen into the system is what determines how low levels drop. The high water events that flooded and shaded vegetation last year resulted in some die-offs prior to fall, but the extended ice and snow cover this winter was the final blow.”
Memphis Lake was rehabilitated in 2002, stocked with fish, and had recently become known as a hot fishing spot for largemouth bass, large bluegill, redear sunfish and channel catfish. Then, during the winter of 2007-08, the lake experienced a severe die-off. “While there are still plenty of bluegill, they are very small and almost no largemouth bass were found,” Porath said.
“We have seen several cases before of severe die-offs in our full rehabilitation reservoirs. When we refill the reservoirs after rehabilitation, the expansive stands of vegetation supply a tremendous amount of food for the fish population, which responds by producing above average growth and quickly gets the fishery back online. But, often fish numbers temporarily exceed the carrying capacity of the system until mother nature steps in and provides a correction,” Porath said. “The timing of this natural correction with a severe winter probably contributed significantly to the situation at Memphis. It is unfortunate because we expected a stellar fishing season this year. Now we will have to evaluate the surviving population this spring and adjust our management to get it back on track for the following year.”
“The winterkill at Fremont Lakes SRA Lake No. 4, located in the area’s north complex of lakes, left only a few largemouth bass and a few small bluegill alive,” said Jeff Schuckman, the Commission’s Fisheries Division district supervisor in Norfolk. “And, only a few carp and a few crappie survived the die-off in Lake No. 7/8, also located in the north complex.”
“We had received reports that people had seen some dead fish in Lake No. 16 in the south complex, but when we checked, we found good numbers of healthy largemouth bass, bluegill, crappie and channel catfish, so we think the lake is in good shape. The dead fish the people saw may have been gizzard shad, which is normal in the spring. When we sampled the lake, we didn’t find any white perch in the sample, which is a good sign.”
Schuckman said the Commission has already restocked 2-inch bluegill in Lake Nos. 4 and 7/8 and he expects there may be a few that reach catchable size by this fall, but the majority won’t reach that size until next spring. He also said there are plans to restock largemouth bass this year and any bass salvaged from other lakes will be put into these two lakes.
Schuckman also had good news for muskie anglers who fish Fremont Lakes SRA. He said the Commission recently stocked 25 advanced-size muskies – fish 10- to 15-inches long – in Lake No. 7/8; 75 more in Lake No. 2; and 71 in Lake No. 20 in the south complex. Lake No. 20 had been plagued with severe blue-green algae problems for the past few years, but the lake has been treated with alum, which has apparently eliminated the problem and left the water there “crystal-clear.”
Schuckman said the University of Nebraska-Lincoln and the Nebraska Department of Environmental Quality will monitor water quality in several Fremont SRA lakes this year.