WAUSAU (WAOW) - State fish experts are warning that low levels of oxygen in the Big Eau Pleine Reservoir near Wausau will cause a significant winter fish kill.
The Department of Natural Resources says testing in late January discovered the problem.
Fisheries Biologist Tom Meronek says the fish kill could be more severe than the die-off that occurred in 2009. He says evidence indicates much lower oxygen levels are being found in the reservoir upstream from Highway S than four years ago.
The DNR says that in 2009 many fish were able to avoid the low oxygen zone by seeking refuge upstream.
The agency says it believes the fish kill has already started this winter based on reports from ice fishermen.
Meronek says part of the problem is the reservoir's frozen and snow-covered surface limits or prevents surface air mixing or light penetration so the water is not replenished with oxygen.
The DNR says the Wisconsin Valley Improvement Company has operated an aeration system on the flowage since 1981 and it provides a refuge for fish when oxygen levels are low.
Meronek says the system, which was upgraded in 2010, is not designed to aerate the entire 6,000-acre reservoir.