Quagga mussel

Dreissena rostriformis bugensis · Aquatic life

Underwater · Photo: National Marine Sanctuaries / Public domain (Wikimedia Commons)

InvasiveMollusk (mussel, clam, snail)

Also called Quagga, Dreissenid mussels, Dreissena bugensis

State listing

Idaho: Prohibited invasive species
Oregon: Prohibited
Wyoming: Game and Fish aquatic invasive species

How to identify Quagga mussel

Small mussel usually under 1 1/2 inches
Rounded, fan shaped shell that rolls over if set on its flat side
Pale cream to brown, often with dark rings or stripes
Attaches to hard surfaces with tough threads (byssal threads)
Often grows in thick clusters

Similar species

Zebra mussels have a flat underside with a sharp ridge so they sit upright. Native mussels and Asian clams do not attach with threads.

Profile

Season	Present all year; spawns when water warms.
Starts	Spawns as water warms past about 50 F
Depth	Shallow to very deep water
How it spreads or reproduces	Microscopic larvae (veligers) in boat bilges, live wells and ballast; adults attached to boats, trailers and equipment
Habitat	Lakes, reservoirs, rivers and canals on any hard surface; also lives on soft bottoms and in deeper, colder water than zebra mussels.

Why it matters in a lake

Clogs irrigation systems, pipes and intakes, coats docks and boats and strips plankton from the water. Idaho has worked to eradicate a localized infestation in the Snake River near Twin Falls since 2023; any suspected find must be reported immediately, and boats must be cleaned, drained and dried.