ONTARIO — Quagga mussels, an aquatic invasive species, have been found for the second time in the Snake River at Twin Falls, Idaho, about 60 miles upstream from the Oregon border.

The Idaho Department of Agriculture announced the discovery on Sept. 24.

The quagga mussel is an invasive species that can spread fast and form large colonies that have a variety of harmful effects. These include reducing fish populations and degrading wildlife habitat, and clogging pipes used for irrigation and drinking water.

The mussels were found recently in the Shoshone Falls pool at Pillar Falls and the Twin Falls Reservoir behind a hydroelectric dam.

Quagga mussels were first found in the Twin Falls area in September 2023.

That was the first confirmation of either quagga mussels or a related invasive species, zebra mussels, in the Columbia River Basin, which includes the Snake River.

Neither type of mussel has been found in Oregon water, according to the Oregon Department of Fish and Wildlife.

But quagga or zebra mussels have been found on six boats inspected at stations in Oregon, including a pontoon boat examined at the station in Ashland on Jan. 4, 2024.

The boat was being hauled from Lake Mead, Nevada.

People towing or carrying watercraft into Oregon from another state must stop at any watercraft inspection station that is open for an inspection. Stations are open if large orange “Boat Inspection Ahead,” signs are posted, followed by “Inspection Required for All Watercraft.”

A watercraft is any size or type of motorized or non-motorized boat such as a kayak, canoe, raft, or stand-up paddleboard.

Oregon’s watercraft inspection stations and hours:

• Ontario: I-84 at the Ontario Rest Area. Open daily, year-round, during daylight hours.

• Umatilla: Highway 395 at the Umatilla Port of Entry. Open until Oct. 25, Thursday to Monday, during daylight hours.

• Ashland: I-5 at the Ashland Port of Entry. Open daily, year-round, during daylight hours.

ODFW encourages everyone to take simple actions to avoid spreading aquatic invasive species such as quagga mussels, by following the “clean, drain, dry” process:

• Clean shoes, waders, life vests, boat hulls and engines, trailers and other equipment by removing all visible plants, algae and mud. Use a stiff-bristled brush to clean equipment.

• Drain any accumulated water from boats or gear, including water used in cleaning, back into the lake, stream, or other waterbody from which it came.

• Let boats or gear fully dry before using again.

Since the start of the watercraft inspection stations program in 2010, ODFW has inspected 226,865 watercraft and intercepted and decontaminated 173 watercraft with quagga or zebra mussels.

Idaho attempts to eradicate quagga mussels

After the September 2023 discovery, the Idaho Department of Agriculture used chelated copper in the Snake River to try to reduce the mussel populations.

Water sample results have showed a decline in mussel numbers since the treatment, according to the agency.

Idaho officials are planning a similar treatment in the river this year.