Benthic invertebrates from ninety samples previously taken from the Athabasca River in February and March 1993 were sorted, identified and counted. The wet weight for each identified taxon was measured, and the incidence ofparasitism in immature Chironomidae by mermithid nematodes was recorded. In addition, immature mayflies, stoneflies and caddisflies representative of the fauna that was sampled for tissue contaminant analyses were identified.