Twenty-seven quantitative fish collections and site habitat analyses were performed from October 1985 to April 1988 in the Little Missouri River in Southwest Arkansas. Longitudinal addition of fish species (from 9 to 30) corresponded to downstream change in physical habitat. Species diversity increased from headwaters to midreaches and was positively correlated with increasing stream size, decreasing particle substrate size, depth, and development of alluvial riffle/pool morphology. The prime factor associated with the increasing fish species diversity was the corresponding increase in habitat diversity downstream. Fish feeding guild structure did not change from headwaters to midreaches. Insectivore/herbivore feeding guilds dominated all riffles and shallow pools. Insectivore/piscivore feeding guilds dominated all deep pools. Differences in species diversity among sample reaches progressing downstream was gradual. Diversity was affected by striped bass and spotted suckers migrating from a downstream impoundment on a seasonal basis and by stocked rainbow trout. This study demonstrated that single reach samples would not be adequate to characterize the stream system or its drainage basin when progressing through diverse geomorphology.