Analysis of young fish taken from Gruber’s Grove Bay on Lake Wisconsin show slightly higher levels of mercury compared to similar fish taken from a different location on Lake Wisconsin but levels in both groups of fish are within the same range for mercury as young fish tested across the state.

Water from the former Badger Army Ammunition Plant’s waste water treatment facility was discharged into Gruber’s Grove Bay during the plant’s years of operation. In the 1990s high levels of mercury were discovered in the sediments of the bay as a result of the discharge.

“Higher levels of mercury in sediments in the bay may be a factor but other variables might be involved too, including fish growth rates and water temperature differences between the bay and Lake Wisconsin,” said Department of Natural Resources biologist Jim Amrhein.

Biologists sampled young panfish, mostly one year of age or younger, from the bay as part of a clean-up monitoring effort of the former Badger Army Ammunition Plant. The complete report, Lake Wisconsin Whole Panfish and Mercury Evaluation, is available on the DNR website.

The Army dredged sediments from the bay in 2002 and again in 2006 to remove mercury and other contaminants. Following the second dredging project, the DNR still found elevated concentrations of mercury in the sediment. The department collected panfish from the bay in 2012 to see if there was any significant accumulation of mercury in fish inhabiting the bay following the dredging.

Young panfish were selected because these fish generally remain in the area where they hatched until they grow to larger sizes. Any mercury found in these fish could be assumed to come from the environment in Gruber’s Grove Bay. “While the study can’t say definitively what caused the higher mercury in the bay fish, the department and the Army remain committed to working on the site”, Amrhein said.

Gruber’s Grove is still listed as an “open site” in the U.S. Army’s clean-up effort for Badger. Results of the study have been shared with the Army which currently is working on plans for further work necessary to close out clean-up efforts on the bay.

“We expect that the Army will present a final clean-up plan for the bay soon,” says Amrhein. “The public will have a chance to comment on the plan and the department will prepare a formal response including consideration of any public comments.”

The Gruber’s Grove Bay study was undertaken as a clean-up monitoring effort. It was not part of the state’s fish consumption advisory monitoring program.

Biologists did however sample game fish and panfish from other locations in Lake Wisconsin and the Wisconsin River between Wisconsin Dells and Prairie du Sac in 2012 as part of the state’s fish consumption advisory monitoring program. Based on results of this survey sample there will be no changes to mercury-based consumption advice for persons consuming fish from these waters.

Logo courtesy Wisconsin Department of Natural Resources

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