"The pipeline extension will bypass Lavon Lake containing any zebra mussels in the pipeline until they can be treated and removed at the water treatment plant," says water district spokeswoman Denise Hickey. "The extension will also provide system flexibility and enable emergency access to water from Jim Chapman Lake, Lake Tawakoni and the East Fork wetlands if terminal storage in Lavon Lake was ever compromised." Zebra mussel management, however, will be an ongoing challenge.

Mussels have spread to 600 lakes since arriving in the U.S. in the 1980s, says the Texas Parks and Wildlife Dept. They grow to only about 1.5 in., but can each produce up to 1 million microscopic larvae that attach to boats and trailers. Wildlife officials are mandating owners to clean, dry and drain boats after they have been in colonized waters or face a misdemeanor.

"There is no known way to eradicate them once they are established in a body of water," says Tom Gooch, Freese and Nichols water resources group planning manager. "In the long term, zebra mussels will provide operation and maintenance challenges to our clients."