Amistad Reservoir ‘infested’ with invasive zebra mussels

By | March 21, 2024

Mar 20—AUSTIN — The Texas Parks and Wildlife Department (TPWD) has designated the International Amistad Reservoir in the Rio Grande Basin along the Texas-Mexico border near Del Rio as “infested” with invasive zebra mussels, indicating that an established, reproducing population is present in the lake.

Zebra mussel larvae were first detected in the reservoir in June 2022 in a water sample collected by the National Park Service (NPS) at the Amistad National Recreation Area. Later in 2023, four additional locations were sampled on multiple dates, resulting in the detection of additional larvae.

The NPS conducted further surveys using shore searches, settlement samplers and sniffer dogs to check for established juvenile and adult mussels. Despite several thorough searches, these size classes of zebra mussels were not found in 2022 and 2023.

Unfortunately, zebra mussels were discovered in several places throughout the lake in late February by the Mexican chapter of the International Boundary and Water Commission (IBWC), which operates the Amistad Dam, and by the NPS. Record low water levels exposed previously submerged rocks and facilitated the discovery of the mussels.

“Since zebra mussels were first detected in Texas in 2009 in Lake Texoma on the Oklahoma border, they have contaminated 32 water bodies and have been repeatedly detected in four others,” said Monica McGarrity, TPWD senior scientist for aquatic invasive species. “It is disheartening that they have now spread all the way to our southernmost border, but many Texas lakes remain uninfected, underscoring the importance of boaters doing their part to clean, drain and to dry when they leave a lake, every time.”

In 2021 and 2022, larvae of invasive quagga mussels, a close relative of the zebra mussel, were detected in the lake. It was the first detection of quagga mussels in the state of Texas and at the time the public was notified of the presence of invasive mussels in the lake. Quagga mussels have not been sighted since May 2022 and their status in the lake remains uncertain. TPWD and NPS continue to monitor the lake for the presence of quagga mussels.

Because zebra mussels are usually transported on or in boats, boaters play a crucial role in preventing them from spreading to new lakes. Zebra mussels attach themselves to boats and anything left in the water, including anchors, and can survive out of the water for days, often hiding in crevices where they can escape attention. Their microscopic larvae float freely and are invisible to the naked eye, allowing them to be carried unknowingly in boats in residual water.

TPWD urges boaters to follow these three simple but crucial steps to clean, drain and dry boats and equipment before traveling from lake to lake. Remove plants, mud and debris. Drain all water from the boat and equipment. Once home, open the compartments and let everything dry completely for at least a week, if possible. The NPS has installed cleaning stations at several locations around the lake to assist boaters in their efforts to prevent the spread of invasive mussels.

“We need boaters to help control zebra mussels by making sure they follow this protocol when leaving Lake Amistad,” said Chris Ryan, Superintendent of the Amistad National Recreation Area.

If a boat is stocked in the waters of Lake Amistad or other lakes with invasive mussels, it is now likely carrying invasive mussels or their larvae and poses an extremely high risk for transporting these invasive species to a new lake. Before moving boats that will be in the water at Lake Amistad for a week or more, call the Amistad National Recreation Area at (830) 775-7492 for advice on inspection and decontamination. Additionally, TPWD can be reached for advice at (512) 389-4848 or [email protected].

In addition to the damage that invasive species can cause to aquatic ecosystems, water infrastructure and the recreational experience on lakes, the transport of these organisms can result in legal problems for boaters. Carrying banned aquatic invasive species in Texas is illegal and punishable by a fine of up to $500 per violation. It is also the law that boaters must drain all water from their boat and onboard containers, including bait buckets, before leaving or approaching a body of freshwater. They must also remove all invasive plants from the boat and trailer before leaving a lake.

For more information on how to properly clean, drain and dry boats and equipment, visit TPWD’s YouTube channel for a short instructional video. For more information about zebra mussels and other invasive species in Texas, visit For more information about the Amistad National Recreation Area Invasive Species Program, visit

TPWD and partners monitor for invasive species in Texas lakes, but anyone who spots them on boats, trailers or moved equipment can help prevent new introductions by reporting the sighting to TPWD at (512) 389-4848. Anyone who finds invasive species such as zebra mussels in lakes where they have not been found before can help identify new introductions by emailing photos and location information to [email protected].

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