202 running-water sites in the catchment of the River Rede, a tributary of the River Tyne in northern England, were sampled for invertebrates in 1990. The distributions of water beetle species were investigated using logistic regression with several environmental factors. A number of site structure characteristics were assessed and the presence or absence of silt (as peat or clay) was found to be the most important single variable. Shingle, pebbles, cobbles, boulders and the amount of vegetation present were less important substrate variables. The distance from stream source reflected substrate structure and site gradient was a poor determinant of species distribution. A composite variable, termed the exposure index, was derived from all the site structure characteristics using an ordination and was found to be useful in explaining species distribution. Water pH also affected distributions considerably. Two variable analyses using the exposure index and water pH gave the best explanation of species distribution. The two variables used together were a reflection of productivity and disturbance, the two main components of habitat templates and strategy theory. The distribution of water beetle species in the Rede catchment was a product of these factors, which, in turn, were a product of the geography of the catchment.