Zebra mussels have arrived in Tarrant County. Now what?

Kneeling over a boat slip, Tom Hungerford reaches down and pulls a thick plastic hose out of the murky water.

At first, nothing appears out of the ordinary, but as Hungerford, a Texas Parks and Wildlife fisheries biologist, runs his fingers through a clump of mud, he finds tiny shells.

A quick inspection confirms they’re the dreaded zebra mussels, an invasive species that litters beaches, clogs pipes and attaches to boats.

Texas Parks and Wildlife recently announced that zebra mussels, which first arrived in North America in the 1980s, are now in Eagle Mountain Lake and Lake Worth.

They were first reported at Eagle Mountain on May 18. At Lake Worth, they’ve now been discovered near the Lake Worth dam, along the upper reaches of the lake in the Fort Worth Nature Center and under the Loop 820 bridge at Arrow S Park.

“It didn’t take me long to find them,” Hungerford said. “They’ll attach themselves to any hard surface they can find.”

Now that the little mussels have arrived, there are questions about what will happen next.

Will it be similar to Lake Texoma, Lake Ray Roberts and Lake Belton, where the zebra mussel populations soared?

Robert McMahon, biology professor emeritus at the University of Texas at Arlington, has been studying zebra mussels for years, and he isn’t sure what will happen.

“It’s hard to say, to tell you the truth,” McMahon said. “You can’t make a prediction right now. The population is in the very early stages of infestation. The question is whether they’re going to have explosive growth like Ray Roberts and Texoma.”

‘Boom and bust’

While there’s a good chance the population will keep increasing at both lakes, it may not last forever.

Christopher Churchill, a hydrologist with the U.S. Geological Survey, said there was a rapid buildup of zebra mussels at those three Texas lakes — Texoma, Ray Roberts and Belton — that was followed by a sudden decline.

“We’ve seen this boom and bust happen at these lakes but for different reasons,” Churchill said. “At Texoma, the population there experienced a crash during the 2011 drought. The population was very large but has not recovered to pre-crash levels. In Ray Roberts we saw a very large population, but the population crash occurred there because of flooding.”

There can be costly consequences when zebra mussels arrive.

The city of Denton and the North Texas Municipal Water District, which is based in Wylie and serves a number of Dallas suburbs, have both spent millions of dollars because of zebra mussels.

During the height of the drought in 2009, the North Texas Municipal Water District couldn’t move water from Lake Texoma because it was determined it would be violating the Lacey Act, which prohibits moving invasive species across state lines.

Getting the water flowing again required an agreement among Texas and Oklahoma, with an assist from Congress.

The district also spent $300 million to build a new 46-mile pipeline to bypass Lake Lavon and pump the water directly into its water treatment plant, where any mussels would be killed. The pipeline opened in June 2014.

Denton may eventually spend close to $5 million dealing with zebra mussels in its pipelines that run from Lake Ray Roberts and Lake Lewisville. Denton first encountered zebra mussels in Lake Ray Roberts, where the razor-sharp shellfish got into a quarter-mile pipeline from the reservoir to Denton’s water treatment plant.

“The biggest problem is when they die off and we have debris accumulation where they tend to accumulate in low-lying areas,” said Tim Fisher, water division manager for the Denton water department.

Denton is also taking precautions for its 9-mile pipeline from Lake Lewsiville, where zebra mussels have also been found. In that case, chemical treatments will likely be used to prevent the mussels from getting established inside the pipeline.

But Fisher said water providers are going to need to be prepared if they take water out of infested lakes.

“I think every entity is probably going to be a little different in regard to their vulnerabilities,” Fisher said.

‘It’s covered with them’

In Fort Worth, the city’s water department has already said it may look at having divers check its intake system at Lake Worth later this year.

The Tarrant Regional Water District has been preparing for zebra mussels for years in its design for the $2.3 billion Integrated Pipeline from East Texas to Tarrant County.

At Lake Bridgeport and Eagle Mountain, TRWD will look at a variety of steps to protect pipelines, said David Marshall, TRWD’s director of engineering and operations support.

“We’ll look at re-coating,” Marshall said. “You can add a coat where they won’t accumulate in the lift systems. We’ll be changing maintenance procedures and anticipating they will get in some pipelines. That could include running chlorine year-round through the pipelines.”

Mark Ernst, TRWD’s water quality manager for the western division, said it takes time to understand the impact of zebra mussels.

The invasive species was first confirmed in Lake Bridgeport in 2013.

Because the lake is full, some might think the population has dropped, Ernst said. But that would be misleading.

“It seems like they’re not there if you look around the shoreline, but in reality they’re down about three feet,” Ernst said. “If you dive into the water and pick a rock up, it’s covered with them.”

‘Needs to be constant monitoring’

There are also questions about the effect zebra mussels have on a lake’s water quality. Because they reduce the food supply in a reservoir, they could push out native clams and mussels while reducing the fish population.

“It’s going be 10 years until we know what their impact will be,” said UTA’s McMahon. “We’re just a few years into this. There’s not enough data yet, but we think they might be starving themselves out by removing all of the plankton and nitrates and phosphates out of the water. But there needs to be constant monitoring.”

The mussels could help improve water clarity in some lakes, but that’s not necessarily a good thing in Texas waters.

One other issue is the razor-sharp shells. When they die, they can litter shorelines making it impossible to walk barefoot. They can also provide an unpleasant surprise for swimmers as they wade into a lake if they’re just underneath the surface attached to rocks or other hard surfaces.

While no one knows what will happen at Eagle Mountain and Lake Worth, Churchill, the USGS hydrologist, said entities should be ready in case the population explodes.

“If there’s a rock or beer can or fishing pole, they can make great use of it,” Churchill said. “It can be a very rapid increase. It’s almost exponential. Then, just as rapidly, they can crash.”

This story was originally published July 15, 2016 at 4:05 PM with the headline "Zebra mussels have arrived in Tarrant County. Now what?."