Scientists have found a single zebra mussel larva and traces of mussel DNA in Lavon Lake, officials said Tuesday. Lavon is the sixth Texas lake where either adults or larvae of the troublesome mussels have been found.
Officials say boaters were probably a factor in spreading the mussels to lakes Texoma and Ray Roberts, and downstream to Lewisville, Bridgeport, Belton and now Lavon.
The routine sampling that revealed the larva in Lavon also found traces of mussel DNA in Grapevine Lake, and for the first time, in lakes Fork and Tawakoni, officials said. Those three lakes are part of the Dallas Water Utilities’ network of supply lakes, although Lake Fork is a future supply source.
Zebra mussels, native to Eastern Europe, propagate at incredible rates, with females producing up to 1 million eggs a year. They have few natural predators in North America. The mussels compete with native species for food, and can filter enough water each day to change a lake’s ecology. They blanket almost any stable surface in thick, almost impenetrable layers. And so far, even the Texas heat hasn’t been enough to stop them.
The discovery of the larva and DNA in Lavon isn’t a big surprise — experts have expected it almost since an established population was found in Lake Texoma in 2009. That’s because the North Texas Municipal Water District, which serves 1.6 million customers north and east of Dallas, used to pump water from Lake Texoma and then let it run down Sister Grove Creek into Lavon Lake as part of its water supply.
Federal officials ordered the district to stop pumping from Texoma, on the Red River, to prevent the spread of mussels into the Trinity River system. The water district resolved the problem by building a $300 million pipeline extension and treatment facility, scheduled to go online this spring.
The plan seems to have worked, at least as far as Lavon is concerned.
After the mussels were found in Texoma, Texas Parks and Wildlife crews descended on Sister Grove Creek and did what they could to destroy any mussels in the waterway, said Brian Van Zee, regional director of the Texas Parks and Wildlife Department’s inland fisheries division.
“That held the mussels off for a couple of years,” Van Zee said. “So that was good. Everyone was on pins and needles for some time. Hopefully this is an indication that we’re being somewhat effective in limiting the mussels’ spread.”
Unfortunately, the mussels managed to find a way into the Trinity system anyway, probably by hitching a ride on a boat moved from an infested lake to Lake Ray Roberts on the river’s West Fork. The mussels are now established and breeding in Ray Roberts and adults have been found downstream in Lewisville Lake, said Dr. Christopher Churchill, project chief for the U.S. Geological Survey’s zebra mussel monitoring program.
If further surveys reveal an established population at Lavon, officials say, the mussels could migrate downstream to Lake Ray Hubbard as well.
“The data we collected from Ray Roberts and the greenbelt section of the [Trinity’s] Elm Fork support that movement,” Churchill said. “When you have a source population, you do look downstream.”
But all that requires more surveys of the lakes and proof that the Lavon larva wasn’t a solitary hitchhiker. Finding DNA or even mussel larvae might just be an indication that boaters aren’t doing a good enough job scrubbing and drying their boats before they move from an infested lake to one considered mussel-free.
Churchill and members of his team will be back at Lavon on Wednesday to see if they can confirm their findings with more samples.
The discovery of a larva and mussel DNA won’t pose an immediate problem for the North Texas Municipal Water District, which uses Lavon as its major reservoir, spokeswoman Denise Hickey said.
Lake water goes to the district’s water treatment plant, which would remove mussels as part of the process, Hickey said. The major long-term concern would be the impact of the prolific little shellfish on water intake pipes.
The new Lake Texoma pipeline extension should provide some answers.
“Once that supply is restored and water is coming in, we’ll be able to see whether the velocity of the water is strong enough to keep adults from attaching to the pipes,” she said.
“We really don’t know what our maintenance will be.”