US Army Corps of Engineers
Mobile District Website

Public Service Announcements

Zebra Mussels Found in Holt Lake on the BWT River

Published Jan. 4, 2021

MOBILE, Ala. – Zebra Mussels have become established in Holt Lake on the Black Warrior & Tombigbee River. They have only been found in small numbers on other parts of the Navigation System. First sighted in 2017, in small numbers and isolated areas on the Black Warrior & Tombigbee River, they are now prevalent on Holt Lake.

Most Zebra Mussels are thumbnail size, but they can grow up two inches long and are usually found in water down to 30 feet deep. They have an elongated “D” shaped, pointed, thin shell with a zebralike pattern of stripes. Unlike native mussels that burrow in sand or gravel, Zebra Mussels spend their adult lives attached to hard objects under water such as: rocks, metal, wood, fiberglass, Styrofoam, PVC, plastic, concrete, aquatic plants, shells of native mussels and crayfish. They can cluster together in colonies of hundreds of thousands per square meter. They are the only fresh-water mussel that attaches itself to solid objects.

In addition to potentially altering the native ecological system, Zebra Mussels can also disrupt water withdrawal operations by clogging water intake pipes. This has caused problems with some lakeshore municipalities and industries, power plants, farms and irrigation systems that have experienced a rise in Zebra Mussels.

Zebra Mussels can affect recreation activities as well. They can accumulate and grow in water intakes of both inboard and outboard boat motors, causing engines to overheat. Boats should not be left in infested water for extended periods of time. With regular use, engine heat will keep them from colonizing inside most engine parts. They attach quickly to boat hulls and can affect boat handling capability, reduce fuel efficiency, and slow speed.

Young Zebra Mussels are about .02 inches long. If a boat hull feels grainy or gritty, it could be covered with small Zebra Mussels. The microscopic larvae can be unknowingly transported in bilges, engine cooling systems, minnow buckets, live wells and anywhere else water is trapped.

If you frequent Zebra Mussel infested waterways, take precautions to prevent transporting them to un-infested waterways.

If they get introduced into your lake the establishment of significant populations will likely take three or four years. Once they become established you will have to learn to live with them.

Please help keep this pest out of your lake. If you find a Zebra Mussel please collect it and contact your nearest U.S. Army Corps of Engineers Office.

For more information visit the Black Warrior & Tombigbee website and on Facebook at @BlackWarriorTombigbee or call at (334) 289-3540.