Zebra mussel invasion creeps south, hits major Texas lake
Troublesome zebra mussels have continued their march south through Texas, with state officials saying they have now infested Lake Amistad, a key reservoir on the Rio Grande.
Texas Parks and Wildlife Department confirms that Amistad, which sits on the border of the United States and Mexico near Del Rio, now has an “established, reproducing population” of zebra mussels in the lake.
Zebra mussels were first detected in Texas in 2009 in Lake Texoma, on the Oklahoma border. Since then, they have infested at least 32 bodies of water throughout the state, according to state officials, including Canyon Lake in Comal County and Medina Lake, west of San Antonio.
The invasive species can wreak havoc on an ecosystem, disrupting the food chain and increasing water clarity, which also can aid vegetation growth. They form dense colonies on hard surfaces, such as docks, pipes and anchors, and also attach to boats, which is most often how they are moved from one lake to the next.
Zebra mussel larvae were detected at Lake Amistad in June 2022 in a water sample collected by the National Park Service, Texas Parks and Wildlife officials said. The National Parks Service, which runs the Amistad National Recreation Area, followed up with shoreline searches, detection dogs and settlement samplers, which are used to monitor mussel growth. They found no settled juvenile or adult mussels in those searches, but again found larvae in more samples in 2023.
Late last month, the mussels were detected at several sites in the lake by both NPS and the Mexican section of the International Boundary and Water Commission, the binational agency that operates the Amistad dam. “Record low water levels exposed previously submerged rocks and facilitated the discovery of the mussels,” Texas Parks and Wildlife officials said.
Amistad is at historically low levels, with its surface about 66 feet below full, according to data from the Texas Water Development Board.
“It is disheartening that they have now been spread all the way to our southernmost border,” Monica Mcgarrity, Texas Parks and Wildlife senior scientist for aquatic invasive species, said in a written statement.
Quagga mussel larvae, another invasive species related to the zebra mussel, also have been detected in Lake Amistad in 2021 and 2022, but have not been identified in the lake since, making their status uncertain, Texas Parks and Wildlife officials said.
Boaters “play a critical role” in stopping the spread of zebra mussels, according to the state agency. The species can attach to boats or other equipment, then survive for days out of water. “Their microscopic larvae are free-floating and invisible to the naked eye, meaning they can be transported unknowingly in residual water in boats,” the state agency said.
Boaters should remove all plants, mud and debris and drain all water from their boats and gear, allowing everything to dry for at least a week before moving from one lake to another.
Boats stored at Lake Amistad are now likely to be carrying the mussels or larvae, and pose “an extremely high risk for transporting these invasive species to a new lake,” Texas Parks and Wildlife officials said.
Boaters should contact Amistad National Recreation Area at 830-775-7492 for guidance on inspection and decontamination before moving boats that have been stored in the lake. The state agency also can provide guidance at 512-389-4848 or Aquaticinvasives@tpwd.texas.gov.
“It is disheartening that they have now been spread all the way to our southernmost border.” Monica Mcgarrity, Texas Parks and Wildlife senior scientist for aquatic invasive species