Zebra Mussels & Other Invaders

Zebra mussels look like small clams with a D-shaped shell. They usually have dark and light-colored stripes. When they are very young, they look like pepper and feel like sandpaper on a smooth surface. Mature zebra mussels are generally the size of a fingernail.The zebra mussel is one of the most economically damaging aquatic organisms to invade the United States. Its destructive power lies in its sheer numbers and its ability to attach itself to solid objects like water intake pipes, propellers, boat hulls, dock pilings, submerged rocks and even other aquatic animals. Colonies of zebra mussels clog filters, pipes, and pumps, and threaten native invertebrates, fish and wildlife. Zebra mussels consume food other species need and can completely change the ecology of infested waters. They can also ruin boat engines by growing in the cooling system intakes and blocking water flow, and can jam steering equipment.

For more information on zebra mussels:

Montana Mussel Response

United States Geological Survey’s page on zebra mussels

Wikipedia Excellent information, especially on the history of the critter’s spread

Montana Department of Fish, Wildlife, and Parks’ page on zebra mussel

Quagga Mussel

You don’t want to meet dreissena rostriformis bugensis. First found in the Great Lakes a quarter century ago, and slightly larger than its inch-long relative the zebra mussel (left), the quagga (right), is indigenous to the Ukraine’s Dneiper River basin, which drains into the Black Sea. It is a filter feeding bivalve that clogs pipes, fouls pumps, covers pilings and rocks, displaces native mollusks, reproduces rapidly, and causes enormous economic damage while profoundly perturbing native ecosystems. The quagga mussel likes cold water.

The quagga hitched rides on boats and trailers and now inhabits the American West. Flathead Lake is still quagga-free — but the mussel is now firmly established in Lake Mead, where millions were discovered in 2007. Lake Mead is next to Highway 93, so these destructive little creatures now have a direct route to Flathead Lake.

More information:  USGS Quagga mussel fact sheet

Eurasian Watermilfoil

Eurasian watermilfoil is a submersed, perennial aquatic plant with leaves arranged in whorls of four around the stem. Each leaf is finely divided into many paired leaflets, giving the plant a delicate, feathery appearance.

This aquatic weed is highly invasive and competes aggressively with native aquatic plant species, thereby reducing biodiversity. Dense Eurasian watermilfoil infestations can severely impair swimming, boating, and fishing. When the plant grows in dense mats, water quality and fish abundance and distribution are harmed.

Eurasian Watermilfoil in Noxon and Cabinet Gorge Reservoirs

Eurasian watermilfoil is now present in Montana in Noxon Reservoir and across the state line in Idaho. It could easily make the transfer to the Flathead Lake region on an angler’s boat. There are, however, simple actions that boaters can all take to prevent the spread of Eurasian watermilfoil and other aquatic invaders.

More information visit the United States Department of Agriculture website on invasive watermilfoil.

Help Prevent the Spread

Before leaving any waterbody:

  • Remove all plants, sediment or animals from your boat and trailer.
  • Drain all water from your boat, including from the motor, live well and bilge. Do not transfer any water from one waterbody into another.
  • Never release live bait into a waterbody or transport aquatic animals from one waterbody into another. Always discard unwanted bait with household trash in the landfill. Likewise, dispose of fish carcasses with trash.

Before launching your boat:

  • Wash your boat, trailer and all fishing gear and equipment. High pressure hot water is best.
  • Air dry your boat and equipment for as long as possible between fishing trips.

If you find Eurasian watermilfoil or a suspicious mussel:

  • Note the date and location where the sample was found
  • Store a piece of the plant or mussel in rubbing (isopropyl) alcohol.
  • Contact your local Montana Fish, Wildlife and Parks office (Region 1 – Flathead area at 752-5501) or call the Aquatic Nuisance Species Coordinator at 406-444-2448 as soon as possible. The earlier we detect a new infestation the better.

Aquatic Invasive Plants