In August 1995 six rusty crayfish (Orconectes rusticus) colonized with zebra mussels (Dreissena polymorpha) were captured in small-meshed fyke-nets set as part of a fish sampling effort at Peter's Marsh and Long-Tail Point Wetland in lower Green Bay. The number of mussels per crayfish ranged from 16 to 431 and the length of the zebra mussels ranged from 1.2 to 12.0 mm with a mean of 3.6 mm. Mussels colonized virtually all areas of the crayfish bodies but the chelae, telson and uropods and thorax were most heavily colonized. Although it is possible that zebra mussels may have positive effects on crayfish populations through associated effects on water clarity, autotroph and invertebrate production, we are concerned that energetic costs or physical constraints caused by attached zebra mussels may be detrimental to crayfish in the Great Lakes.