Invasive zebra mussels, scourge of Great Lakes, reach Texas

By Bill Hanna

Just a few feet from shore, a large rock is covered with them. A quick scan of the shoreline turns up many more.

This invasive species, an import from Eastern Europe, has long been spreading across the United States. The Great Lakes have been dealing with it for years, and now it has reached Texas.

So far, it has been found only in Lake Texoma and Sister Grove Creek, a tributary that the North Texas Municipal Water District uses to send water from Texoma downstream to Lake Lavon.

“The best way to avoid introduction is to prevent it from ever getting there in the first place – of course, the consequences once it gets established are pretty great,” said Robert McMahon, a professor emeritus in the University of Texas at Arlington department of biology who has studied zebra mussels since 1990.

The fear is the resilient mollusks and their larvae will be washed downstream into Lake Lavon, where they could spread throughout the Trinity River basin, creating havoc with pipelines and intake valves and threatening native species.

While scientists have tried to kill them off in Sister Grove Creek, the North Texas water district has stopped pumping for the past 18 months from Lake Texoma. Biologists have been successful in killing off most of them.

What makes the task more daunting is that there is another, perhaps more likely way for zebra mussels to spread: via boats that are hauled from infested lakes. That is what is thought to have happened at Lake Texoma.

“My feeling is it’s inevitable we’re going to see them here,” said David Marshall, engineering services director of the Tarrant Regional Water District. “The only question is, will it be in two years or 10 years?”

Scientists can’t say for sure what will happen if they get established in Texas, but the evidence in other states isn’t pretty. Zebra mussels have changed the ecosystems of lakes and ruined beaches for swimmers by depositing razor-sharp shells along the shoreline.

For those who maintain reservoirs, such as the U.S. Army of Corps of Engineers and the Tarrant Regional Water District, there is concern that they could choke intake valves and screens. That could force agencies to spend untold dollars retrofitting old systems with copper screens, creating regular scraping programs and pumping higher doses of chlorine through pipelines to prevent clogging by the mussels.

“It is a difficult challenge because they are so resilient,” said Randy Cephus of the Corps of Engineers’ Fort Worth District. “That’s why preventive measures are so vitally important. Once they get a toehold, they can multiply very rapidly. They’re very hard to get rid of.”