Three-quarters of the world's crayfish fauna are found in the US and Canada. Small natural ranges, habitat disturbance, and introduced crayfish species threaten many species, and nearly ½ are imperiled. Naturally small ranges are considered the leading factor for crayfish vulnerability to loss, yet species with small ranges have received little research attention. Orconectes saxatilis is a rare crayfish species with a range restricted to the upper Kiamichi River watershed in southeastern Oklahoma. We examined the distribution, habitat use, and life-history characteristics of O. saxatilis and 2 sympatric crayfish species in the upper Kiamichi River watershed to determine factors that might limit its distribution. Surveys for O. saxatilis expanded its known range and confirmed its restriction to tributaries of the upper Kiamichi River. Orconectes saxatilis showed a strong affinity for riffles, contrary to previous data, whereas Orconectes palmeri longimanus, a regionally abundant sympatric species, showed an equally strong affinity for pools. Tributaries of the upper Kiamichi River are intermittent, and surface flow typically ceases in late summer and early autumn. During dry periods when habitat was limited to disconnected pools, O. saxatilis aestivated beneath cobbles and boulders in dry riffles. The strict use of riffles by O. saxatilis and its need for habitat conducive to aestivation probably contribute to its small range and put this species at risk. Year-round monitoring of populations susceptible to imperilment is needed to make informed conservation decisions. For O. saxatilis and other imperiled crayfish species, conservation efforts should emphasize identification of habitat types required for species survival, avoiding alterations to those habitat types, and protecting natural flow regimes.