Fight against invasive water plant moves to Oxbow Slough at Minto-Brown Island Park

Crews will begin combating an invasive water plant at Minto-Brown Island Park's Oxbow Slough starting Monday.

Visitors to Minto-Brown are advised to stay out of the slough during treatment times to avoid possible exposure. Treated plants will be marked with a blue-green dye to show areas treated. The herbicide is absorbed by the plants within 24 hours, and the blue dye may remain visible for weeks.

The effort to reduce Ludwigia hexapetala, also known as Uruguayan water primrose, is part of a new five-year partnership between the city and Willamette Riverkeeper.

City officials said the effort mirrors the successful project completed in Willamette Slough over the past four years. Last year, teams planted more than 12,500 native trees and shrubs in the Willamette Slough where Ludwigia had been removed to provide shade and reduce the habitat for the sun-loving invasive plant.

Treatments on Oxbow Slough are scheduled to begin Monday through Aug. 2 with a second series of treatments scheduled Aug. 26 through Aug. 30.

Ludwigia forms in dense mats that limit recreation and reduce habitat for wildlife.

"While the plant may appear attractive with its yellow flowers, it poses significant ecological threats to the Willamette River by choking waterways, degrading water quality, and harming native fish and wildlife," city officials said.

Specialists have labeled the species the "worst invasive aquatic plant in the state." They suspect it came to Oregon through aquarium and aquatic garden trades and spread rapidly in the past decade.

Future work includes planting native plants in and around Oxbow Slough. Treatments will continue through the summer of 2028.

City officials said the goal is to reduce the plant’s population to such a degree that additional herbicide treatment will not be necessary once the project is complete.

The Oxbow Slough is near the playground and Parking Lot #3 at Minto-Brown Island Park. It is a popular spot for fishing and kayaking, but Ludwigia's presence can make the latter difficult depending on the time of year.

The slough and surrounding area are home to several varieties of fish, otters, great blue herons, ospreys, bald eagles, cormorants and more.

Further information on the city's efforts to restore the sloughs is available online at cityofsalem.net/community/natural-environment-climate/environmental-planning-management/streams-wetlands/restoring-the-willamette-river.

For questions, comments and news tips, email reporter Whitney Woodworth at wmwoodworth@statesmanjournal.com, call 503-910-6616 or follow on X at @wmwoodworth