Prior studies outlining the impact of zebra mussels (Dreissena polymorpha) on unionid populations have reported that the unionid subfamily, Lampsilinae, including the genera Ligumia and Lampsilis, are more sensitive than Anodontinae, such as Pyganodon, to colonization by zebra mussels.  A unionid survey was conducted before and after zebra mussel introduction into Douglas Lake (Michigan) to determine the impact of zebra mussels.  Live unionids were collected within a one meter radius of three transects at depths of 1, 2, 4, 5.5, 7, 8.5 and 10 meters.  Unionids were identified to species, measured in length and attached zebra mussels were removed, counted and measured in length.  Populations of Ligumia nasuta, Ligumia recta and Pyganodon grandis have increased following zebra mussel introduction, whereas the abundance of Lampsilis siliquoidea has not changed.  Although unionid species did not influence the size or number of attached zebra mussels, the number of attached zebra mussels was positively correlated to unionid shell length, with Ligumia larger than Pyganodon.  Transect location influenced the number of attached zebra mussels, however sample depth did not.  These data suggest that short term changes in the unionid population of Douglas Lake in response to zebra mussel colonization, vary amongst unionid genera.