The colonization patterns of Baetis along with those of periphytic diatoms, which form a major component of their diet, were simultaneously examined in Carp Creek, a spring-fed stream located in Cheboygan County, Michigan. Distinctly different diatom floras were observed in two upstream areas of a stream which were located relatively close in proximity (100 meters). Established artificial substrates at Site 1 [sunny, slow mean current velocity (26 cm/sec)] exhibited significantly greater diatom densities than substrates at Site 2 [shaded, faster mean current velocity (35 cm/sec)]. Diatom standing crops on established substrates at Site 1 were up to three times as great as estimates at Site 2. Volumetric transformations served to minimize differences between sites, with diatom biomass at Site 1 being approximately twice as great as that at Site 2. Significantly greater densities of both Achnanthes minutissima and Cocconeis placentula were found at Site 1 over Site 2 on all sampling dates, with the exception of the initial, seven day sampling period. Other major diatom taxa (Fragiliaria pinnata, Achnanthes lanceolata and pennate diatoms) did not exhibit significant differences in standing crop between sites. Niche breadth calculations, used to quantify the evenness of diatom distribution through time, revealed an increase in evenness of diatom distribution through time at Site 2 in comparison to a decrease in evenness at Site 1. Low evenness at Site 1 is primarily attributable to the high relative abundance of A. minutissima (65% total standing crop as compared to 31% at Site 2).