Zebra Mussels
How GBRA is working to monitor and protect lakes in the Guadalupe River basin
Info about Zebra Mussels
What are Zebra Mussels and where do they come from?
Adult zebra mussel (Source: GBRA)
Zebra Mussels are an invasive, fingernail-sized mollusk that is native to fresh waters of Eurasia. Their name comes from the dark, zig-zagged stripes on each shell.
The first Texas infestation of this species was discovered on Lake Texoma in 2009. By the end of 2020, Texas Parks & Wildlife Department (TPWD) had confirmed the detection of Zebra Mussels in five Texas river basins, and at least 31 Texas lakes, with 23 water bodies designated as "infested" with an established, reproducing population. The Guadalupe River basin is currently the southernmost range of this invasive species.
After a watercraft in the Cranes Mills Marina area of Canyon Lake showed signs of Zebra Mussels in 2017, TPWD officials conducted larvae testing and determined zebra mussels were present in the lake. This positive finding placed all of the reservoirs downstream of Canyon Lake at risk of invasion, as Zebra Mussel larvae disperse downstream.
Guadalupe-Blanco River Authority (GBRA) and TPWD staff now regularly conduct sampling at designated areas at Canyon Lake, the downstream reservoirs and along the Guadalupe River .
What are aquatic invasive species?
Aquatic invasive species are organisms that invade ecosystems beyond their natural, historic range. Their presence may harm native ecosystems or commercial, agricultural, municipal utilities and/or recreational activities that are dependent on these aquatic resources. ( US Fish & Wildlife )
Images: Adult Zebra Mussel infestation on water intake at Canyon Lake (Source: GBRA)
How do they affect us?
Zebra Mussels have sharp shells and multiply rapidly. They negatively impact ecosystems in many ways, and can become beach hazards, damage boats and boating equipment, and clog water intakes.
Utilities, such as drinking water supply providers (like GBRA) and power plants, must invest significant financial resources to remove Zebra Mussels from water intake pipes that have become infested and clogged.
The risk of ecological effects in the Guadalupe basin are particularly profound due to their propensity to colonize the shells of native mussels and potentially harm unique state threatened species such as the Guadalupe orb (Cyclonaias necki), False spike (Fusconaias mitchelli) and Guadalupe fatmucket (Lampsilis bermanni). Zebra Mussels feed by filtering organic material and microorganisms from the water column. This directly removes food sources for other organisms, disrupting the food chain. It also can increase water clarity, sometimes allowing harmful algae species to bloom.
GBRA Canyon Lake Raw Water Intake Video Inspection (April 2020)
Image at Right: GBRA Western Canyon Water Treatment Plant Intake (Source: GBRA)
GBRA monitoring efforts
What is GBRA doing to monitor the spread of Zebra Mussels throughout our lakes in the Guadalupe basin?
Since Zebra Mussels have been detected in Canyon Lake, through the GV Hydro Lakes to Gonzales, GBRA now focuses its monitoring efforts upstream of Canyon Lake and downstream of Gonzales. TPWD uses the information collected during early detection monitoring events to classify the Zebra Mussel status of water bodies.
This is an interactive map of GBRA Zebra Mussel sampling sites
To zoom in and out on the map click +/- buttons at bottom right
To search for an address click magnifying glass icon at upper left
Sample sites are symbolized by current sampling results
To view map legend click icon at lower left
You can also click on the individual sample site in the map, to see a pop-up table with more detailed information
Positive = adult Zebra Mussels or larvae have been found in samples more than once
Negative (Absence) = no adult Zebra Mussels have been found in samples
Infested = there is an established, reproducing population of Zebra Mussels in body of water
Types of Monitoring
GBRA has proactively collaborated with TPWD to provide early detection monitoring of the species expansion in the Guadalupe River basin.
Settlement samplers are deployed at multiple locations to track the spread of the invasive mussels. These “McMahon-style” and “Portland-style” samplers consist of a steel wool pad, affixed to clear plastic clasps or a 4” perforated PVC pipe.
These apparatuses are hung in the water column and checked at quarterly intervals to document the presence of juvenile and adult Zebra Mussels that selectively colonize their surfaces.
Left: Colonized McMahon sampler at Canyon Park Marina on 11/01/2017 and Right: Colonized Portland sampler at Lake Placid (Source: GBRA)
Veliger and DNA Sampling
GBRA Water Quality Technician Jana Gray conducts sampling for the microscopic veliger larvae of zebra mussels along the hydro lakes system on 11/28/2018 (Source: GBRA)
GBRA and TPWD biologists are monitoring this species even when individuals are too small to see.
GBRA researchers pull 12” wide x 36” long plankton nets vertically through the water columns of Lake Dunlap, Lake McQueeney and Lake Placid during optimal breeding conditions in the spring and fall, as water temperatures reach 16 to 19°C (61 to 66°F).
Water samples collected are sent to TPWD A.E. Wood Fish Hatchery and are analyzed under microscopes to identify the presence or absence of microscopic veligers.
Cross-Polarized Light Microscopy (CPLM)
Microscopic zebra mussels cannot be easily distinguished from native clams under normal lighting (Left Image)
Microscopic zebra mussels have a "Maltese Cross" pattern that is only observable when the shells are illuminated with cross-polarized light (Right Image)
Adult zebra mussels (Source: GBRA)
"The larvae are dispersed on water currents to settle throughout an invaded water body. Once settled, Zebra Mussels reach maturity within one year of life." - Robert McMahon
GBRA mitigation efforts
Once Zebra Mussels were confirmed in Canyon Lake, GBRA began investigating available options to prevent an infestation from affecting the Western Canyon Water Treatment Plant. To address this threat, a comprehensive approach has been established by GBRA to manage and mitigate the impact of Zebra Mussels on the water supply:
Regular Inspections: GBRA has been using a robotic camera system to perform regular inspections of the freshwater intake pipes in Canyon Lake to identify any Zebra Mussel activity.
Cleaning and Maintenance: In early 2024, contractors removed existing Zebra Mussels and cleaned the plant’s wet well and the freshwater intake pipes that extend into Canyon Lake.
Preventative Treatment Process: Following the removal of all Zebra Mussels, an EPA approved treatment process safe for drinking water usage, was added to the freshwater intake pipes. This enhanced treatment process ensures Zebra Mussels cannot continue to inhabit the water intake structures in the future.
Water intakes at GBRA Canyon Lake raw water pump station
What you can do to help
In order to manage and conserve our natural resources and protect outdoor recreation opportunities, Texas Parks and Wildlife Department enforces laws to protect our state waters against the introduction of exotic aquatic species.
For more information, visit TexasInvasives.org . Invasive species that have been introduced into water bodies often travel from one water body to another by "hitching a ride" on a watercraft.
