Monica McGarrity is lying face down at the end of a wood dock at a Lake Conroe marina, dipping a microphone-like device into the water to collect samples and deploying a net that resembles an airfield windsock to gather microscopic particles.
She hopes she doesn't find what she's looking for.
"Wish me bad luck," laughs McGarrity, an aquatic invasive species biologist for the Texas Parks and Wildlife Department.
She's one of two biologists canvassing about three dozen Texas lakes for signs of zebra mussels, an invasive shellfish that's steadily advancing across much of the central and eastern United States and now with a foothold in Texas.
Besides upsetting Mother Nature's balance, the mussels are affecting infrastructure and now changing the way Texans play with their water toys.
Beginning July 1, the Texas Parks and Wildlife Commission expanded a requirement to all Texas lakes and rivers: People leaving or approaching public water must drain all water from their vessels and on-board receptacles, rinse them and dry them. It applies to all types and sizes of boats, personal watercraft, sailboats, kayaks, canoes or any other vessel.
The zebra mussels -- sharp fingernail-size shells with stripes -- attach and multiply on nearly everything from old soda cans, the underside of docks and boats to the inside of pipelines carrying fresh water to utilities, power plants or agriculture.
"More or less, once they attach, that's it," McGarrity said. "Then they filter, filter, filter. All of the stuff I'm catching here. They filter away and that's how they make the water more clear. They're eating all the nutrients that the fish eat."
The clearer water lets in additional sunlight, allowing undesirable plants to thrive and alter the food chain. That depletes the native fish population.
Their razor-like shells also can make beaches treacherous and less attractive for visitors, hurting local economies.
Recreational water users say the new regulations are likely to be an inconvenience but worth it to protect the lakes.
"People may just have to accept it and take on the responsibility," Terry Finley, 64, of Montgomery, said as he filled his WaveRunner with gasoline for a day on Lake Conroe.
The cleaning is intended to remove traces of zebra mussels and keep them from being transferred to another body of water.
"Once they're in, it doesn't take long," said Robert McMahon, a University of Texas at Arlington biology professor who's studied the critters for years. "I don't want to be saying it's doomsday. It's just they're economic and ecological pests. They plug up water works and that can cost millions."
That's what happened in Lake Texoma, where Parks and Wildlife officials announced in 2009 the first confirmation of a living zebra mussel in Texas. At the 89,000-acre reservoir providing water to North Texas residents, a $300 million project designed to fix damage from clogged pipelines and keep the zebra mussel from spreading was finished in May.
The mussels moved on anyway, likely hitching rides on boats that hadn't been cleaned properly.
They've since been found in at least four other North Texas lakes, plus Lake Belton in Central Texas, the first of the Brazos River basin lakes.
"They especially like to get into pipes and dark crevices," McGarrity said. "And once they get into pipes, they attach to other shells and completely cover the openings."
A single female can produce a million eggs in a year.
The species came from Ukraine, spread more than a century ago with development of canals in Europe and then is believed to have been introduced to the U.S. in the late 1980s aboard a cargo ship near Detroit.
Texas game wardens will enforce the cleaning rule but "you can't be at every lake every day," Brian Van Zee, regional director of the state wildlife agency, acknowledges. "It's very difficult."
The mussels' steady march south in Texas brought McGarrity to Lake Conroe, one of more than a dozen lakes from Austin to Houston she's testing. Laboratory tests and examination under a microscope eventually will confirm whether Conroe is the species' newest home.
"To our knowledge so far, this lake is not," she said.