AUSTIN (KXAN) — Invasive zebra mussels have been found in two more Central Texas lakes: Lake Lyndon B. Johnson, located northwest of Austin, and Lake Pflugerville northeast of Austin.

Lower Colorado River Authority staff found about a dozen young and adult mussels near the Thomas C. Ferguson Power Plant near Horseshoe Bay on July 29. They’ve also found the mussels in other areas on Lake LBJ, including near Wirtz Dam, McNair Park and Kingsland Community Park. Texas Parks and Wildlife Department’s Monica McGarrity says the mussels are expected to spread downstream to Lake Marble Falls.

“Only boats can move this invasive species upstream to uninvaded reservoirs and downstream dispersal is inevitable,” McGarrity said. She’s the TPWD’s senior scientist for aquatic invasive species management. “Zebra mussels haven’t yet been found in Lakes Buchanan and Inks, upstream of Lake LBJ, but their introduction closer to these lakes reinforces how critical it is for boaters to take steps to prevent their spread.”

Zebra mussels have also been found at Lake Pflugerville, which serves as a water supply reservoir.

The city of Pflugerville says it found the invasive species on the intake pipes that flow water into Lake Pflugerville from the Colorado River last September. The city hired divers to clean the pipes regularly and help mitigate the spread of the zebra mussels, but they eventually made their way into the lake.

Officials say people need to help stop the spread of zebra mussels by making sure they clean, drain and dry their boats, personal watercraft and gear after being out on the water.

“A single mussel-fouled boat or barge can carry thousands of zebra mussels and cause a new lake to become infested,” McGarrity said.

In Texas, it’s illegal to possess or transport Zebra mussels, which are invasive and can harm native species, cover surfaces with their sharp shells, damage boats and motors and clog water intakes. In February, people in downtown and south Austin experienced smelly water after Austin Water chemically flushed one of its temporarily offline raw water tunnels that had been infested with the mussels.

As of August, officials say 17 lakes in five Texas River basins are considered to be infested with established populations of zebra mussels.

John Higley, CEO and Principal Scientist at EQO, which works with government agencies on treatment plans for zebra mussels, says the invasive species is eating good algae in central Texas waters, bu leaving the toxic blue-green algae alone, creating space for it to grow.

“You’re filtering out all their native competitors, and so that creates a nice ground for them to be able to breed,” Higley said.

Higley says he doesn’t believe the zebra mussels have been at Lakes LBJ and Pflugerville long enough to help breed toxic algae this year.

“But next summer if the problem isn’t controlled, we could see that,” Higley said.

As Higley works with local agencies to come up with a treatment plan, he says people have to take responsibility and better clean their boats.

“It’s bad stewardship for your environment and for your city to just willy nilly and move from one lake to the next,” he said. “It’s just the height of selfishness.”

In addition to properly cleaning boats after leaving the lake, kayakers and paddleboarders should exercise just as much caution in rinsing and drying their watercrafts. Higley says even swimwear could spread zebra mussel larvae, so it’s important to wash swimsuits after visiting the lake, as well.