In the 1980s, invasive quagga and zebra mussels hitchhiked on ocean vessels from Eastern Europe to northeast North America. There, the thumbnail-sized bivalves proliferated, clogging water intake pipes, crusting boats, wreaking havoc on ecosystems and causing billions of dollars in damage. Measures were taken to prevent their westward spread, but in 2007 quaggas arrived, eager to reproduce, in Nevada's Lake Mead (HCN, 3/5/07, "Wish you weren't here").
Containment measures such as inspecting and cleaning boats have helped keep the mussels out of most Western waterways, although they've been found in a dozen water bodies in Colorado, Utah, Arizona, Nevada and California. But this spring, quaggas were spotted for the first time at marinas on Lake Powell. The Associated Press reports that the Lake Powell quaggas "weren't close enough (together) to reproduce," so there may be time to stop their colonization of the reservoir.