CBS News, among other sources, is reporting that zebra mussels (Dreissena polymorpha) have been eradicated from a quarry in Virginia. Eradication is a pretty strong word, but state officials seemed confident in their announcement, made earlier this week, noting that this is the only known successful eradication of the invasive mollusks. How did they do it? Turns out they dosed the entire quarry with potassium chloride, a molluscide. While people are likely to be skeptical about claims of eradication, the tests that were done have shown a zebra mussel death rate of 100%, and the effects of the potassium chloride are expected to last thirty years. However, this kind of treatment is unlikely to be feasible in natural water bodies where native mussel species are also present.
A page from the Virginia Department of Game & Inland Fisheries provides more information about the project, including this environmental impact report (.pdf). The ISW first reported on the Milbrook Quarry zebra mussel invasion back in March 2003, and then again in November 2003.