Brazilian elodeaegeria densa, is a freshwater, perennial plant that looks like a larger, more robust version of its native relative, elodea canadensis (waterweed). Brazilian elodea has green serrated leaves that grow in whorls with tiny white flowers that float on the water’s surface. The plant, once commonly found in pet stores and nurseries, is no longer sold in Washington. The Department of Ecology suspects that most invasions have occurred after people dumped aquarium contents into lakes.

Listed as a state noxious weed, the invasive characteristics of this plant allow it to rapidly overtake freshwater lakes and streams. Its dense growth interferes with recreation, navigation, fishing, and wildlife habitat. Brazilian elodea has infested 27 western Washington lakes. It was introduced into the Duck Lake Waterways System in Ocean Shores sometime in the early 1990s. At that time, lake residents and the City of Ocean Shores adopted a nonchemical approach to weed management. The city focused its efforts on stocking infested waters with sterile (triploid) grass carp–a plant-eating fish. Over time, lake residents also pulled weeds by hand and even invested in building their own mechanical harvesting machine to reduce the noxious weed problem. Still, Brazilian elodea continued to thrive and colonize much of the shallow waterway system, making it less usable.

In 2005, residents and city staff began to explore the idea of using aquatic herbicides to manage the rampant growth. While Brazilian elodea is notoriously difficult to eradicate, aquatic herbicides can effectively control this species (a removal rate of up to 99 percent). In early 2007, city officials treated Duck Lake using two herbicides and by summer, the lake and its waterways were relatively free of Brazilian elodea. With the infestation under control, lakeside residents and the public were able to enjoy the lake for boating, swimming, and other recreation. In the future, the grass carp present in the lake may be able to stem new growth of Brazilian elodea. If not, judicious herbicide treatments should keep Brazilian elodea populations under control.