The zebra mussel (Dreissena polymorpha) is a highly invasive freshwater bivalve species that poses a significant threat to aquatic ecosystems and human infrastructure across North America. Since their introduction to the Great Lakes in the 1980s, these organisms have spread rapidly, causing ecological damage and economic losses. Their ability to filter large volumes of water and attach to submerged surfaces in dense colonies makes removal challenging, yet necessary, for property owners and water managers. Preventing their further spread is a continuous effort required to protect uninfested waterways.
Identifying the Threat and its Impact
Adult zebra mussels are typically small, reaching a maximum length of about one and a half inches. They are characterized by a distinct D-shaped shell with a flattened underside and often display a striped pattern of alternating yellow/tan and brown coloration, which gives them their name. The life cycle begins with microscopic, free-swimming larvae called veligers, which are invisible to the naked eye. These veligers settle after two to three weeks and use sticky fibers called byssal threads to anchor themselves permanently to any firm surface.
The threat posed by these mussels stems from their prolific nature and ability to colonize surfaces, often reaching densities of thousands per square meter. Economically, the primary impact is biofouling—the clogging of water intake pipes, distribution systems, and cooling systems used by power plants and municipal facilities. This colonization restricts water flow, increases corrosion, and necessitates high annual mitigation and maintenance costs. Ecologically, zebra mussels are highly efficient filter feeders, removing massive amounts of plankton from the water column. This disrupts the aquatic food web by starving native species and increases water clarity, which can cause excessive growth of submerged aquatic plants and contribute to toxic algal blooms.
Physical and Thermal Removal for Personal Equipment
Removing established zebra mussels from personal watercraft, docks, and recreational gear primarily relies on mechanical and thermal methods. Adult mussels attached to hulls, trailers, or dock pilings can be physically removed by scraping or high-pressure washing. High-pressure spraying (3,000 to 3,500 psi) is effective for dislodging the mussels and should be applied systematically across the entire surface. For sensitive areas like the motor’s lower unit or transducers, a softer brush may be necessary alongside the water spray.
Thermal treatment is the most effective way to kill the organisms, including microscopic veligers hidden in crevices and internal components. Hot water is lethal to zebra mussels, with temperatures of 140°F recommended at the point of contact to ensure mortality. For large surfaces, a low-flow rinse should maintain contact for at least 10 seconds. Interior compartments like live wells or bilges can be flushed with 120°F water for 90 to 130 seconds. Flushing the engine’s cooling system with hot water can also kill mussels that have colonized the intake grate and internal passages.
When hot water or pressure washing is not available, the second viable option is complete dehydration and desiccation. After removing the equipment, all visible mussels, plants, and mud must be scraped off and disposed of in the trash. The equipment must then be allowed to dry completely, exposed to direct sunlight if possible. Drying time varies significantly based on local temperature and humidity, ranging from five days in warmer conditions to 15 to 20 days during cooler or wetter months to ensure all mussels and veligers are killed.
Chemical and Large-Scale Control Methods
Widespread infestations in closed systems or large water bodies often necessitate the use of chemical controls applied by professional agencies and requiring specific permits. These methods treat municipal infrastructure, power plant intakes, or entire quarantined quarries where non-chemical removal is impractical. One common approach involves the use of molluscicides, such as potassium chloride (KCl) or copper compounds. Potassium chloride works by interfering with the mussel’s respiratory system, causing death by asphyxiation.
Potassium chloride is generally considered less harmful to non-target aquatic organisms, including fish, compared to other biocides. Copper compounds are also used because of their toxicity when ingested by the mussels, though concentrations must be carefully monitored to avoid harming other organisms. Other specialized techniques include carbon dioxide (CO2) injection, which displaces oxygen to suffocate the mussels, and targeted aeration, which creates localized conditions unsuitable for survival. These large-scale treatments are complex, demanding precise concentration control and prolonged exposure times, and are not suitable for private application.
Steps for Preventing Mussel Spread
The most effective strategy for preventing the spread of zebra mussels is consistently following the “Clean, Drain, Dry” protocol every time watercraft or gear moves between water bodies. The first step is to clean all visible aquatic plants, animals, and mud from the boat, trailer, and any equipment. This inspection must be thorough, as juvenile mussels and veligers can be easily missed in hidden areas.
Next, completely drain all water from the watercraft before leaving the access area. This means pulling the boat plug and draining the bilge, live wells, ballast tanks, and engine cooling systems. Veligers are microscopic and can survive in small amounts of residual water, making this step paramount to preventing transport. Finally, the equipment must be allowed to dry completely before launching into another water body. Adequate drying time ensures the death of any remaining veligers or adults, and laying out gear ensures full desiccation.