Butomus umbellatus may conjure up images of a hippopotamus belly, but in reality, it is flowering rush, an aquatic invasive plant species that poses a grave threat to the Columbia River Basin’s aquatic ecosystems.
Flowering Rush is not native to the Pacific Northwest and its eradication is a focus for the US Army Corps of Engineers’ Walla Walla District.
“Flowering rush is an aggressive colonizer and can grow in a wide range of freshwater habitats,” Bret Walters, Chief of Planning and Environmental Branch for the Walla Walla District, said. “Once it’s established, flowering rush dominates native plants and can even take root in areas that were previously free of any vegetation, leading to significant ecological changes.”
These impacts are of particular concern for native salmon populations, whose livable habitats are reduced when flowering rush forms dense stands in previously un-vegetated waters. This disadvantages salmon that require open water to rear their young and advantages predatory fish that spawn in vegetated waters.
Furthermore, predators utilize flowering rush as camouflage, ambushing salmon that venture too close to these stands.
“The combination of reduced rearing habitat and increased predatory exposure can reduce juvenile salmon populations and lower salmon recovery rates, so controlling and eradicating flowering rush is a priority to protect salmon and other native populations,” Walters said.
The spread of flowering rush has significant impacts for humans as well, impairing recreational opportunities in areas where dense infestations grow adjacent to the shoreline and docks.
“These growths interfere with boat propellers and become a nuisance to those trying to swim or fish,” said Walters.
Flowering rush also supports habitat for the great pond snail, a host for the parasites that cause swimmers' itch. Moreover, infestations in irrigation canals can significantly reduce water flow, leading to costly removal measures that impact farmers and agricultural production.
Recognizing the potential severity of these impacts, the Walla Walla District has partnered with the states of Washington, Oregon, Idaho and Montana to implement a cost-share program that encourages state and federal environmental managers to take a proactive approaches in treating and controlling flowering rush infestations.
Through the program, the Corps reimburses the states for 50% of their yearly costs for coordinating and establishing early detection monitoring, control and treatment, and post-treatment monitoring for flowering rush infestations occurring off federally managed lands.