The Texas Parks and Wildlife Department in June announced a juvenile zebra mussel and microscopic larvae were found at the U.S. Army Corps of Engineers-operated lake. Zebra mussels are an invasive species that pose an ecological and economic threat, damage boats and threaten a city’s water supply by clogging pipes.
The lake is soon expected to be classified as infested—or having an established, reproducing zebra mussel population—according to TPWD District Fisheries Biologist Raphael Brock. Neighboring Lake Lewisville is already classified as an infested lake.
“We are just waiting on a few more sightings of zebra mussels before we classify it as infested,” Brock said. “It’s a high likelihood it will be considered infested in six months or so due to the zebra mussels reproduction.”
Both Lake Lewisville and Grapevine Lake are used for water supply for different municipalities, and Lake Lewisville is the main water source for Lewisville, according to Lewisville Director of Public Services Keith Marvin.
Although the city of Lewisville contracts with Dallas Water Utilities for its water supply, it runs its own water intake facility. Marvin said the zebra mussels have posed a threat to the flow of water through the intake facility if the city had not taken any action.
Lewisville Superintendent of Water Production Kelly Rouse said the city was proactive in putting measures that would help prevent colonization on the intake facility’s pipes.
“We purchased equipment that prevents the zebra mussels from adhering to the pipes,” Kelly said. “It went online in June 2017, and we have not had any problems,” he said.
Marvin said even if the zebra mussels made it into the intake facility it would not affect the treated water, but that removing a colony from a pipe is very labor-intensive and costly.
“Bypassing is not a problem because then [zebra mussels] are filtered out in our treatment process,” he said. “Any organisms, dirt, grit or zebra mussels is filtered out of our water. Building up colonies on our infrastructure is the problem we were attempting to deal with.”
Rouse said the city sends divers every year to inspect and verify that are no colonies on the facility’s pipes.
An invasive species
Zebra mussels were first discovered in Texas at Lake Texoma in 2009 and since then have spread to several lakes.
“[Lake Texoma is] where the whole infestation came from,” Brock said. “More than likely it was spread from boaters who do did not clean their boats. However, we do have a lot of lakes that are connected via pipes and a lot of lakes that have downstream flows into another lake, which are all ways that zebra mussels can spread as well.”
Brock said Lake Lewisville’s infestation was the result of Lake Ray Roberts’ downstream flow.
“Lake Lewisville is below Ray Roberts so during the flood years the zebra mussels basically just flowed directly from Ray Roberts to Lewisville,” he said.
Texas state law requires owners to drain water out of a boat before leaving the water, Brock said. He said TPWD has been working to teach the public to also clean a boat with high-pressure water and soap and let it dry for at least a week before moving to another lake that is not infested by the mussels.
“Once it is in the lake [there is] not much you can do,” he said. “The cost to do anything to combat their numbers in the ecosystem is cost-prohibitive. So the best thing you can do is keep them from spreading.”