Methodological Detail from David Lewis' Ph.D. Dissertation and Lewis and Magnuson (2000)

We surveyed each lake once for snails and several variables that potentially influence snail distribution. Prior to sampling, lake habitat was determined by mapping around the entire shoreline of a lake at 30 m intervals or by consulting habitat maps (Petrie et al. 1993) that we confirmed for accuracy. Sample sites were chosen randomly, stratifying by habitat type.