Great Lakes freighters may have to treat ballast water to curb invasive species

Invasive zebra mussels are seen on wooden pilings from a dock at the University of Wisconsin-Madison Center for Limnology on Lake Mendota in Madison, Wis. Students and researchers removed the dock before the onset of winter. Here, doctoral student Mike Spear scrapes the dock's wooden pilings for zebra mussels to count the number that are attached and compare the number to previous years. His research helps track the density of mussels in the lake.
Coburn Dukehart | Wisconsin Watch
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