OSHKOSH – Officials with the state Department of Natural Resources have assessed the creamy white, decomposing organic material, sometimes mixed with brown material, that has been collecting on parts of the west shore of Lake Winnebago.
The white substance, observed, photographed and sampled by DNR staff early Monday, has been identified as a form of decaying blue-green algae, mixed with other common forms of decaying algae that are brown in color.
These decomposing algae are not related to the AP Nonweiler industrial fire Monday night in Oshkosh which resulted in the release of a non-toxic white substance – titanium dioxide mixed with fire-fighting water – that was highly visible in the water Monday evening.
The titanium dioxide, used as a whitener in paper production as well as in toothpaste and some foods, did not cause environmental damage and did not result in a significant fish kill. The substance will rapidly dissipate.
DNR fisheries biologists are also investigating reports of a fish die-off in the lake. Most of these fish, seen along the shoreline and out in the lake, are sheepshead, or drum. DNR fisheries staff also collected some dead fish – including a few game fish – near Fond du Lac. Samples from these fish are being analyzed.
While some fish mortality is common right after ice out, due primarily to low oxygen levels caused by decaying organic material, the larger-than-usual die-off of sheepshead could be the result of another cause, possibly bacteriological or viral. DNR fisheries and water quality staff do not believe the die-offs are related to the decaying algae collecting along shorelines.
Kendall Kamke, fisheries supervisor in Oshkosh, said there is no reason, based on information in hand, to be overly concerned about the health of the overall fishery.
DNR fisheries and water quality staff said the lack of snow on the Lake Winnebago ice this past winter allowed algae to bloom and die under the ice. With warmer temperatures, the dead algae became buoyant and rose to the surface where the breeze pushed it toward the west shore. This accounts for reports from sturgeon spearers this past February who observed a large amount of white material in the lake that broke up into tiny crystals when they tried to skim it out.