Oregon on alert after discovery of invasive mussel species in Prineville Reservoir

A single dead adult quagga mussel was discovered on the shoreline of Prineville Reservoir on June 6 during a routine aquatic invasive species survey. This marks the first documented finding of the highly invasive freshwater mussel species in or near an Oregon waterbody.

Despite this initial discovery, subsequent intensive surveys, water samples and environmental DNA tests conducted by Portland State University did not detect any other invasive mussels.

The presence of quagga mussels poses a serious environmental and economic threat to Oregon and the Pacific Northwest. Since their introduction in the 1980s, these small, non-native freshwater mollusks have rapidly reproduced, clogging water intake systems, outcompeting native species and disrupting recreation and aquatic habitats and infrastructure.

On June 6, crews from Portland State University Center for Lakes and Reservoirs conducted surveys at Prineville Reservoir and nearby waterbodies as part of their regular aquatic invasive species surveillance work. Surveyors located the single dead adult quagga mussel on shore in sand about one meter above the waterline. They collected the mussel and contacted the Oregon Department of Fish and Wildlife (ODFW), Ore. State Marine Board (OSMB) and the Oregon Invasive Species Council, following established protocols. It is unknown at this time how the quagga mussel ended up on the shore of the reservoir.

Since the June 6 detection, ODFW and OSMB, along with federal, state and local partners, have been operating under the Oregon Invasive Freshwater Mussel Rapid Response Plan. They have formed a Unified Command to coordinate continued surveillance, sampling and outreach efforts for boaters in central Oregon and across the state. Keith DeHart, ODFW Aquatic Invasive Species Coordinator, emphasized the seriousness of the situation. “We are taking this finding extremely seriously, but also cautiously as we work to confirm what we're seeing at Prineville Reservoir,” DeHart said. “We are coordinating closely with our state, federal, tribal and local partners and preparing to move quickly based on the evidence we find. Our top priority is protecting Oregon's waters while making sure every action we take is grounded in the best available information.”

During surveys conducted by PSU crews in late May and early June 2026 at Prineville Reservoir, technicians completed six dock inspections covering 182 meters and surveyed 22 shorelines totaling nearly 1,500 meters. They also performed 57 mussel larva tows, with 53 boat-based and four stationary tows near the dam, filtering more than 296,000 liters of water overall. All surveys and laboratory results from the water samples, as well as environmental DNA samples, were negative for invasive mussels.

On June 18, ODFW staff inspected two floating restrooms and their associated buoys, as well as two moored vessels on Prineville Reservoir. All checks followed standard invasive species protocols and no invasive freshwater mussels were detected on any structures or vessels during the survey.

Recreational boats are a significant source of freshwater invasive mussel spread in the United States. Inspections have intercepted boats fouled by live invasive mussels before launching in Northwest waters multiple times in recent years. In April, ODFW staff at the Ashland Boat Inspection Station found golden mussels on a watercraft traveling from the Sacramento River Delta to Oregon and decontaminated the boat before it reached an Oregon waterbody.

To help prevent the dispersal of freshwater invasive mussels, boaters should follow the "Clean, Drain, Dry" protocol for all boats, trailers and other equipment after leaving a lake or stream. Boaters are also required to stop at check stations for inspection. These stations are currently located in Brookings, Ashland, Klamath Falls, Ontario and Umatilla. A roving check station will also be at boat ramps around Prineville Reservoir and central Oregon periodically in coming weeks to inspect watercraft for invasives. Check stations and other invasive species surveillance are funded by proceeds generated by the Aquatic Invasive Species Permit and Waterway Access Permits.

Public outreach, including watercraft inspections, is increasing. Inspections, educational materials and signage are intended to reinforce the "Clean, Drain, Dry" protocol with Oregon boaters. The public is encouraged to report any suspicious sightings to the Oregon Invasive Species Hotline at one‑866‑INVADER or online at https://oregoninvasiveshotline.org to support ongoing monitoring and early detection efforts. DeHart noted that continued public involvement is crucial. “Continued vigilance and cooperation from the public are vital to protecting Oregon's waters and keeping recreation areas open,” DeHart said.

Monitoring teams will continue routine intensive sampling efforts to ensure early detection and rapid response if quagga mussels are present. The Oregon Department of Fish and Wildlife and its partners will continue to monitor the situation at Prineville Reservoir and regional waterbodies, allocating additional resources as needed. Expanded water and shoreline surveys are being conducted to facilitate early detection. Prineville Reservoir remains open to the public, as inspections showed no visible mussels or signs of invasive freshwater species on structures or vessels.