Considerable spatial and temporal variability was detected in the environmental conditions in 30 coldwater springs in southern Ontario, Canada. Using standard pyramidal emergence traps, a total of 86 insect species was recorded from these springs (not including the Chironomidae). These represented nine taxonomic groups, among which the Limoniidae (Diptera) was the most diverse with 38 species. Fifty-five per cent of all species recorded had a low frequency (found at three or fewer sites), and only for very few of these rare species were more than 10 individuals m-2 collected. Interannual differences were also apparent. Continuous sampling over time showed that emergence records from a single year, on average, contained only around 50% of the total number of species obtained during the entire study. Species-environment relationships analyzed by Canonical Correspondence Analysis indicated that temperature and discharge correlated most strongly with insect community similarity among spring sites. The prospects for developing regional typologies of coldwater springs, based on their environmental conditions, and the implications of species loss to the continuity of function of coldwater spring ecosystems are discussed.