Zebra mussels to the rescue. (Biotechnology).

Oh, those clever Dutch engineers. They've turned zebra mussels into local environmental heroes.

In the United States, immigrant zebra mussels (Dreissena polymorpha) have been setting up ultradense colonies that rob food from native aquatic ecosystems and even clog intake pipes to water-treatment and industrial plants. However, it's their propensity for crowding that makes these reviled bivalves so attractive for water-purification systems, says Mathijs G.D. Smit of TNO, an applied research institute in Den Helder, the Netherlands.

On April 29, at a meeting of the Society for Environmental Toxicology and Chemistry in Hamburg, Germany, Smit described his group's installation of two small mussel-filled test filtration tanks at a pool located in a Dutch zoo's pelican exhibit. The pool usually turns rank and ugly in the summer when bird feed stimulates excessive growth of algae. The mussels removed up to 69 percent of those algae along with other suspended particles.

In a second project, Smit and his colleagues floated boxes of mussels in a stream from which agricultural fertilizers feed into a lake, causing summertime algae blooms. The shellfish took in a portion of the fertilizer chemicals but didn't prevent the blooms. Nevertheless, Smit says, the local water authority intends to pursue the zebra mussel tactic as part of a water-purification strategy.

But what if the mussels get loose? "We don't care," Smit told Science News. Dutch river bottoms and lakebeds are silty muck. Because mussels must attach to hard surfaces, he says, "they can never become a plague here."