The city of Waco began its war Tuesday against zebra mussels in Lake Waco, fighting against time and water temperature as much as the invasive critters themselves.

City crews and divers spent the day unrolling giant sheets of pond liner and covering the lake floor around the Ridgewood Country Club boat ramp, where the mussels were confirmed earlier this month.

Dressed variously in waders, shorts and wet suits, about a dozen men worked with two motorboats to drag the half-ton PVC tarps into the water. They weighted down the tarps with sandbags in an attempt to smother the invaders in an area the size of a football field.

“This is crazy, but I hope it works,” Waco water quality program manager Tom Conry said. “If it works, that buys us several years.”

What is at stake is the ecological balance of the lake, as well as possibly hundreds of thousands of dollars a year that would be needed to keep zebra mussels from clogging up city water intakes.

Zebra mussels are a Eurasian species that have come to dominate many Midwestern lakes and rivers. They reproduce best at a temperature between 50 and 77 degrees, so city officials are scrambling to get the tarps in place as that temperature range arrives. The tarps will remain for four months, long enough to kill the mussels by depriving them of oxygen and food.

State biologists involved in the project said Lake Waco is the seventh lake in Texas to be infested with the dreaded mussels, but they are hoping it will be the first where the infestation can be reversed.

City of Waco lake monitors discovered the zebra mussels near the ramp in late September. Texas Parks and Wildlife Department on Oct. 1 confirmed them and discovered more on a barge that a contractor was using to make dock repairs for Ridgewood.

Wading chest-high in the water and directing the tarp placement Tuesday afternoon was Brian Van Zee, TPWD regional director for inland fisheries.

“Brian, do you have any zebra mussels you aren’t using that we could get pictures of?” Conry called to Van Zee.

Van Zee fished around in the water and hauled ashore a basketball-sized chunk of concrete with two dime-sized mussels attached. He pried one off, pointing out the telltale stripes and the fibers, called byssal, that allow the mussels to attach to hard surfaces.

“Most native mussels don’t have that ability,” he said.

In addition, zebra mussels have an exceptional ability to filter plankton out of the water for food, and their reproduction cycle is much faster than other mussels, Van Zee said. Within months of being discovered at Lake Belton in September 2013, the mussels were distributed throughout the lake.

But TPWD monitoring this month at Lake Waco found no DNA evidence that mussels or their mobile larvae had spread beyond the boat ramp area.

Van Zee said the mussels discovered by the ramp are adults and may have fallen off the bottom of the barge, which was covered with more than 1,000 zebra mussels.

The barge, owned by James Phillips of Belton, reportedly was transported from Lake Belton to the Ridgewood boat ramp in July. The mussels on the barge and in the water could not have grown from larvae in three months, city and state officials said.

Van Zee said TPWD crews will continue regular DNA sampling around the lake during the life of the project to see if larvae have escaped into the body of the lake.

Joe Bernosky, city of Waco utility director, said scientists elsewhere are working on ways to control and possibly eradicate zebra mussels, most likely through biological methods. In the meantime, he hopes Waco can demonstrate that early intervention against zebra mussels can work.

“It’s never been done on this scale before,” he said.

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