Presents results of an experiment conducted in artificial streams (flumes) in which the growth of periphyton (algae) was studied in relation to phosphorus concentrations in the water. The goal of the study was to determine whether periphyton growth in the Athabasca River was phosphorus limited and whether the degree of phosphorus limitation varied from a similar study conducted in fall 1993. The experimental flumes were located on site, adjacent to the Athabasca River at Hinton. The four-week experiment consisted of four treatments: a control of zero phosphorus addition and three experimental levels of 1, 10, and 25 micrograms per litre of phosphorus. Results include relative specific growth rates as indicated by measuring the build-up of chlorophyll a, the level at which growth rate saturation occurred, and phosphorus concentrations required to reach maximum biomass levels in spring.