Quagga Mussels Detected for First Time in a Texas Reservoir

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AUSTIN – The Texas Parks and Wildlife Department (TPWD) reports that invasive quagga mussels have been detected for the first time in Texas. The quagga mussel discovery was made by National Park Service (NPS) staff at the International Amistad Reservoir in the Rio Grande basin along the Texas-Mexico border near Del Rio.

Quagga mussels are a close relative of the zebra mussel, which has invaded 33 Texas lakes across six river basins since it was first introduced in Texas in Lake Texoma in 2009. In addition to being the first detection of quagga mussels in Texas waters, this is also the first finding of any invasive mussel species in the Rio Grande basin.

“This detection of invasive quagga mussels is a very unfortunate first for Texas,” said Monica McGarrity, TPWD Senior Scientist for Aquatic Invasive Species. “Quagga mussels can inhabit greater depths and are also able to settle on soft substrates like mud or sand in addition to hard surfaces like rock or infrastructure—unlike zebra mussels—meaning they can colonize more of the lake.”

“Quagga mussels are very prolific and can form larger populations that can have greater effects on the lake ecosystem overall, especially in deep lakes,” added McGarrity. “Even the lakes that already have zebra mussels are at risk of having quagga mussels introduced and monitoring of these lakes for signs of quagga mussels will be necessary.

The NPS staff monitor Amistad Reservoir for early detection of invasive mussels using sampling for plankton (microscopic organisms) to detect their larvae and conducts settlement and shoreline sampling to survey for juveniles and adults. In June 2021, a single quagga mussel larva was detected and confirmed by DNA testing at Diablo East. In May, August, and September, single quagga mussel larvae were detected at a second site, Rough Canyon.

The NPS staff have been actively monitoring Amistad Reservoir for zebra and quagga mussels since 2014. Early detection monitoring can assist in preventing spread to other water bodies as well as providing an early warning for mitigating impacts on infrastructure for facilities using raw surface water. Currently, NPS employees conduct monthly inspections from docks and structures at several sites on the reservoir.

Since July 2021, NPS staff have also conducted multiple shoreline surveys using mussel detection dogs. To date, the NPS has not detected juvenile or adult mussels that might indicate population establishment. NPS staff will continue monitoring for quagga mussel larvae as well as juvenile and adult mussels and any future population establishment and will be exploring potential opportunities for containment should a full infestation develop.

TPWD is designating the reservoir as “positive” for quagga mussels. Positive status indicates mussel larvae have been repeatedly detected, but no juveniles or adults have been found and there is not yet evidence of a fully established population. The detection of quagga mussel larvae underscores the critical need for lake users to follow TPWD’s prevention guidelines when visiting Amistad Reservoir.

In addition to reducing the risk of further introductions of quagga mussels that could contribute to establishment, there is a need to prevent the introduction of zebra mussels and other aquatic invasive species. The NPS and TPWD encourage all visitors to follow the “Clean, Drain, and Dry” actions for watercraft and equipment before entering and after leaving the lake.

Because quagga mussels are present in other areas of the U.S. in the Great Lakes region and some western states, there was already a risk that boats could transport them to Texas lakes. However, their introduction into a Texas reservoir significantly increases the risk they could be transported by boats and introduced into other waterbodies in the state. The TPWD and partners will continue monitoring at-risk waterbodies for early detection of both zebra and quagga mussels. Prevention signage will also be updated at Amistad Reservoir.

Quagga mussels, in the same manner as zebra mussels, are often transported to new lakes by boats. Therefore, TPWD and partners will continue public awareness outreach efforts to encourage boaters to take steps to clean, drain, and dry their boats and decontaminate boats with attached mussels to prevent the spread of these invasive species.

"Unfortunately, invasive mussels have now spread to 34 Texas lakes, with 28 fully infested, but there are far more lakes that still haven’t been invaded and are at risk,” said Brian Van Zee, TPWD Inland Fisheries Regional Director. “Each boater taking the necessary actions to clean and drain their boat before leaving the lake and allowing compartments and gear to dry completely when they get home can make a big difference in protecting our Texas lakes.”

Because invasive mussels are most often transported on or in boats, boaters play a critical role in preventing their spread to new lakes. Invasive mussels attach to boats, and anything left in the water, including anchors, and can survive for days out of water, often hiding in crevices where they may not be seen easily. Their larvae are microscopic and invisible to the naked eye and can be unknowingly transported in residual water in boats. Boaters are urged to clean, drain, and dry their boats and gear before traveling from lake to lake. Remove plants, mud, and debris, drain all water from the boat and gear, and then open compartments once you get home and allow everything to dry completely for at least a week if possible.

If you have stored your boat in the water at a lake with invasive mussels or purchased a boat that has been stored on one of these lakes, it is likely infested with invasive mussels and poses an extremely high risk for moving these invasive species to a new lake. Before moving your boat that has been stored on a waterbody known to have either zebra or quagga mussels or if you purchase a boat from out-of-state and have questions, call TPWD at (512) 389-4848 for guidance on decontamination. Other equipment stored in infested lakes such as barges, docks, hoists, and pumps etc. are also potential vectors for spreading invasive species so those items also need to be fully decontaminated before transporting to another waterbody.

The transport of aquatic invasive species can result in legal trouble for boaters or transporters. Transporting prohibited invasive species in Texas is illegal and punishable with a fine of up to $500 per violation. Boaters are also required to drain all water from their vessel and onboard receptacles, including bait buckets, before leaving or approaching a body of fresh water.

Additionally, anyone who spots invasive mussels on boats, trailers or equipment that is being moved should immediately report the sighting to TPWD at (512) 389-4848.

TPWD and partners monitor for invasive mussels in Texas lakes, but anyone who finds them in lakes where they haven’t been found before should report them immediately by emailing photos and location information to AquaticInvasives@tpwd.texas.gov.

A status map showing all lakes where invasive mussels have been found in Texas can be viewed online. For more information on how to properly clean, drain and dry boats and equipment, visit the TPWD YouTube channel for a short instructional video.

Information for marinas and owners or buyers of boats stored in the water on lakes with zebra mussels can be found online. To learn more about invasive mussels and other invasive species in Texas, visit tpwd.texas.gov/StopInvasives.