Carl Pearson dusts cobwebs off his boat as he prepares to push off into Lewisville Lake for some summer relaxation. At a nearby boat ramp a sign reminds him he'll need to clean off more than cobwebs when he returns to shore: It's illegal to transport zebra mussels from the lake.
The warning sign is part of an awareness campaign wildlife officials are waging to halt the migration of the pesky non-native shellfish that have spread this summer to more North Texas waters after already causing billions of dollars in economic damage in more than two dozen other states. The mussels clog inflow pipes of water suppliers, build colonies inside boat engines and can hurt lakeside businesses by making beach-walking hazardous with their sharp edges.
"It's big-time money," said Bob McMahon, a biologist at the University of Texas at Arlington who developed monitoring and risk assessment programs for the mussel with funding from by the U.S. Fish and Wildlife Service. "It's by far the most costly aquatic freshwater invasive species that's ever been introduced into United States waters."
The prolifically breeding mussels arrived in Texas in 2009 at Lake Texoma, about two decades after they were first spotted in the U.S. and quickly colonized all five Great Lakes. Since then mussels or their larvae have spread to three other lakes in Texas, most recently Lewisville and Bridgeport lakes.
Because there are no large-scale environmentally safe methods for eradication of zebra mussels, wildlife officials are trying protect other lakes fed by the Trinity River by requiring people to clean, dry and drain their boats after they have been in colonized waters. The mussels -- whose larvae are invisible to the naked eye -- can expand their range by hitching rides on boats and trailers.
The Texas Parks and Wildlife Department and numerous other entities are also working to educate boaters with an advertising campaign -- including press releases, signage and pamphlets available at all marinas. Those caught transporting or possessing the zebra mussel can be charged with a Class C misdemeanor.
The program's success is largely dependent on the public. Because the state lacks the resources to stringently monitor and enforce its regulations, some boaters question whether the mussels' spread can be stopped.
"Mother Nature has been at this for a while, whether it (the zebra mussel) gets delivered by a bird or by a boat," Pearson said as he swept his boat deck at a Lewisville Lake marina, about 25 miles north of Dallas. "But what you have to do is stem the tide."
The species is originally from the Balkans, Poland and the former Soviet Union. They made their way to the Americas in the 1980s via a ship's ballast water. They were first found in 1988 in Michigan, and within 10 years had colonized all five Great Lakes and the Mississippi, Tennessee, Hudson, and Ohio river basins. They have infested at least 29 states and more than 600 lakes or reservoirs in the U.S.
In Texas, not all lakes have the proper conditions to allow for a sustaining population. Lakes with low calcium levels, for example, don't support the mollusk.
The recent discovery at Lewisville Lake most likely stemmed from contaminated boats. It was made less than a year after the mussels established a population in Lake Ray Roberts, less than 40 miles north of Lewisville Lake.
Other high-risk bodies of water being monitored for possible mussel populations are the Red River, the Elm Fork of the Trinity River, Lake Lavon and two lakes downstream from Bridgeport -- Eagle Mountain and Worth.
The mollusks have already caused problems for some water suppliers in the region dealing with clogged inflow pipes from the thriving mussel population. Last fall crews with the North Texas Municipal Water District, which serves 60 North Texas cities including Frisco and Plano, had to manually clean pipes at Texoma to the tune of $3.7 million, spokeswoman Denise Hickey said.
Businesses that depend on lake visitors could also feel a pinch if the mussels overwhelm nearby beaches and waters with their sharp edges, presenting a danger to swimmers and beach-walkers. Revenue declines could ensue as fewer people bring commerce to the area, but so far few in the Lewisville area appeared overly concerned.
"It's not that big of a deal," said Rafael Daniel, a manager at Sneaky Pete's restaurant. "If you drain your boat and rinse it out, you get zero mussels."