TPWD to Standardize Zebra Mussel Classification System

Steve Lightfoot, 512-389-4701,

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AUSTIN—Texas Parks and Wildlife Department (TPWD) is updating its system of classifying zebra mussel presence in lakes to better describe the level of impact and align with standards used by other state and federal agencies.

The new standards classify lakes as: 1) Suspect if there is one verified detection of zebra mussels; 2) Positive if there are multiple or repeated detections; and 3) Infested if the water body has an established, reproducing population.

Currently, six Texas lakes are classified as infested with zebra mussels: Texoma, Ray Roberts, Lewisville, Bridgeport, Dean Gilbert (a small lake in Sherman) and Belton. Lakes Waco and Lavon, which were previously classified as infested due to repeated detection of zebra mussels or their larvae, have been reclassified as positive under the new system because there is no evidence of a reproducing population.

“Transitioning to this classification system not only helps us to better communicate with other states in the West but also helps us to paint a better picture for the public of what is happening with zebra mussels on our lakes,” said Monica McGarrity, Austin Aquatic Invasive Species Team Leader for TPWD.

For example, according to McGarrity, under the old system Lake Waco was classified as infested. In the fall of 2014, the City of Waco, the U.S. Army Corps of Engineers and TPWD implemented rapid response measures, placing tarps in affected areas to stop the spread of zebra mussels. When the tarps were removed, no zebra mussel larvae or evidence of juvenile settlement were discovered.

“This suggests there may not be a reproducing population in Lake Waco. Only time and monitoring will tell for sure,” she said.

Researchers have found zebra mussel larvae in Lake Lavon on several occasions over the past few years, but similarly to Lake Waco, no juvenile settlement or adult zebra mussels have been detected, so Lavon will also be classified as positive.

“Even though Waco and Lavon are going to be reclassified as positive, we know zebra mussels have been found there and it is important for boaters to remain vigilant about cleaning, draining and drying their boats,” stressed McGarrity.

TPWD and its partners continue to monitor lakes considered high risk for zebra mussel introductions. This year, 12 lakes were downgraded from inconclusive (a status given when zebra mussel DNA is detected or an unverified suspect organism is found) to negative status based on sampling results. Zebra mussel DNA—a warning sign—had previously been detected in these lakes.

Three other Texas water bodies—Lake Fork, Lake Ray Hubbard and Fishing Hole Lake (a small lake connected to the Trinity River below Lake Lewisville)—are classified as suspect after sampling revealed the presence of either larvae or an adult zebra mussel.

TPWD marketing staff, with support from a coalition of partners, has developed a major public awareness campaign aimed at slowing the spread of zebra mussels by reminding boaters to Clean, Drain and Dry their boats, trailers and gear before traveling from one lake to another. The partners in this effort include: North Texas Municipal Water District, Tarrant Regional Water District, City of Dallas Water Utilities Department, Trinity River Authority, San Jacinto River Authority, Sabine River Authority, Brazos River Authority, Guadalupe-Blanco River Authority, Lower Colorado River Authority, Upper Trinity Regional Water District, Water Oriented Recreation District of Comal County and the Lady Bird Johnson Wildflower Center.

“The campaign objectives are to inform boaters about the very important role they play in preventing invasive zebra mussels from spreading and to reinforce the actions they need to take every time they leave the water,” says Carly Montez, Senior Marketing Specialist at TPWD. “Three simple steps can help stop the spread of zebra mussels and also help you stay within the law. Clean, drain and dry your boat, trailer and gear.”

Since zebra mussel larvae are invisible to the naked eye, boaters must drain all water from their boat and all receptacles on board when traveling on a public roadway to or from a public water body in Texas. This regulation applies to all types and sizes of boats whether powered or not: personal watercraft, sailboats, kayaks/canoes or any other vessel used on public waters. Movement from one access point to another on the same lake during the same day does not require draining.

More information on zebra mussels and regulations can be found online at