The byssus protrudes between the two halves of the shell. These threads attach to hard surfaces with a powerful glue that anchors the mussels in place. Small juveniles can actually break away from their attachments and generate new, buoyant threads that allow them again to drift with the currents and find a new home. Beds of zebra mussels in some areas of Lake Erie contain between 30,000 and 70,000 mussels per square meter. Zebra mussels can become established regardless of depth, light intensity, or even winter temperature.
Colonies are rare in wave-washed zones, except for sheltered nooks and crevices.
In most European lakes, the greatest densities are at depths ranging from 6 to 45 feet. Zebra mussels also colonize soft, muddy bottoms. Hard objects, such as pieces of native mussel shells, act as a base for settling veligers. As a few mussels begin to grow, they serve as substrate for additional colonization. In this way, extensive mats of zebra mussels can form on soft lake and river bottoms.