Recreational boaters should be especially on the lookout for aquatic plants and mussels on the hit list. Those species can be unknowingly transported on trailers and boats.
In the plant category, the lead suspects are Hydrilla, Eurasian Watermilfoil, Giant Salvinia and Water Hyacinth.
Hydrilla and Milfoil were imported to the U.S. for use in aquariums in the 1950s. The species entered Florida’s inland waters after being discarded or planted in canals. Hydrilla is now in 28 states and spreading. Milfoil is more climate-tolerant and found nationwide.
Hydrilla and milfoil are mainly introduced to new waters as fragments on recreational boats, their motors and trailers and in livewells. Colonization begins after the fragments are dislodged from a trailer, emptied from a livewell or pumped out of a bilge.
Stem pieces root in the bottom and develop into new colonies, commonly beginning near boat ramps. Once established, boat traffic continues to break and spread Hydrilla and Milfoil. Because of how fast it colonizes and spreads, the plants are difficult to control. Mechanical harvesting is mostly ineffective, leaving chemical herbicides as the only option for controlling it.
Giant Salvinia, a South American aquatic fern, imported as an aquarium plant, is now rapidly expanding in public waters. Plant coverage can double in size in about a week, and the thick mats deplete oxygen content and impede boating and fishing. A single acre can explode to more than 2,000 acres in just 12 weeks. To get that started all it takes are broken plant stems attached to a boat trailer. Giant Salvinia tops the list of problematic plants in Texas.
Water Hyacinth is a floating plant that forms dense rafts in the water. Look for large spikes of lavender-blue flowers, spongy, bulbous leaf stalks and large, rounded leaves. Hyacinth also has a high growth rate, doubling in size in as little as two weeks by sending off short runner stems that develop new plants.
Outside of plants, Quagga and Zebra Mussel invasions have catastrophic impacts in the ecosystems they invade. They clog water intake structures, which greatly increase maintenance costs for water treatment and power plants. Recreational activities on lakes and rivers are adversely affected as mussels accumulate on docks, buoys, boat hulls, anchors and beaches can become heavily encrusted.
The shells of both mussel species are sharp and can cut people, which forces the wearing of shoes when walking along infested beaches or over rocks. Mussels adhering to boat hulls can increase drag, affect boat steering and clog engines, all of which can lead to overheating and engine malfunctions.
The mussels were introduced into the Great Lakes after cargo ships discharged ballast water containing them. Today, they are among the most dangerous of all exotic species, due to their microscopic size and the difficulty of identifying them.