When the glaciers retreated from North America, huge chunks of ice left behind made permanent divots in the Northern Plains. These glacial potholes - now prairie wetlands - provide vital habitat for migrating geese. Strategies to protect the rapidly decreasing prairie potholes from increased development and agriculture will be the topic of a Workshop on Prairie Wetlands Ecosystems, Oct. 3-5 in Bismarck, N.D. Speakers include John W. Meagher, director of the EPA's wetlands division, Thomas Park, from the Bureau of Reclamation in Montana and Paul Hansen, a wetland expert at the University of Montana. The Environmental Protection Agency Region VIII is the main sponsor of the gathering. For information, contact Thorne Ecological Institute, 5398 Manhattan Circle, Suite 120, Boulder, CO 80303 (303/499-3647).