It might be impossible to get rid of them, but it is possible to fight back.
Marble Falls City Engineer Kacey Paul detailed ways the city is protecting its infrastructure from invasive zebra mussels at the City Council meeting May 19.
Measures include installing a screen on the city’s raw water intake in the next week or two to prevent the mussels from entering the system and clogging pipes. The screen’s coating is designed to discourage zebra mussels from attaching. A copper-based molluscicide will be released at the site as well.
At the Lakeside Park beach, the city plans to install Dock Disks along the concrete wall and buoys to discourage mussels from taking hold there. Dock Disks are a brand of 7½-inch foam disks that emit a 7- to 8-foot radius of zebra mussel repellent, which is copper-based. The repellent isn’t harmful to people or fish as used at this level.
“Copper is toxic to zebra mussels, and they can’t detect it,” Paul said. “If you use chlorine, (zebra mussels) can just hold their breath for 45 minutes to an hour, so you have to dose chlorine the full time they’re holding their breath.”
That’s not something the city wants to do in the lake, so copper appears to be a good alternative.
Zebra mussels have been spreading across Texas lakes. In October 2019, the Lower Colorado River Authority reported finding zebra mussel verlingers (mollusk larva) and juveniles in Lake Marble Falls at multiple locations, including Wirtz and Max Starcke dams. By December 2019, Lake Marble Falls was listed by the Texas Parks and Wildlife Department as fully infested.
Since October 2019, the city has performed tests on products and materials at Lake Travis to see which materials are more prone to zebra mussel colonization. One such experiment dangles samples of materials such as PCV plastics, copper, zinc, steel, and other materials in the water to determine which ones the invasive species prefers.
The mussels are here to stay. Not only have there been no surefire eradication measures created since zebra mussels came to the United States in the 1980s from Eurasia, but the warm water, pH, and high calcium in the Highland Lakes make for a comfortable environment for the species, according to Paul’s report.
Though small individually, zebra mussels clump together in large colonies that jam water intakes and amass on docks, rocks, shorelines, boat propellers — just about any surface — which is why boaters are strongly encouraged to drain and clean watercraft and trailers before leaving or entering a body of water.
Zebra mussels can also be sharp. As they accumulate on shores, they can become a hazard to walkers.
Because zebra mussels are filter feeders, the water in Lake Marble Falls might become clearer as the mussel population grows. The downside, environmentally, is that they compete with fish for their plankton food source.
Visit the TPWD’s invasive species website for more information on zebra mussels.