Technical Abstract: An alternative practice to land spreading of manure effluents is to grow crops of algae on the nitrogen (N) and phosphorus (P) present in these liquid slurries. The objective of this study was to determine how algal productivity, nutrient removal efficiency, and elemental composition of turf algae grown in outdoor raceways respond as a function of seasonal changes in light and temperature, carbon dioxide supplementation, and different loading rates of raw and anaerobically digested dairy manure effluent. Algal biomass was harvested every 4 to 12 days from replicate 30 square meter pilot-scale algal turf scrubber raceways using daily loadings of manure effluent corresponding to rates of 0.3-2.2 g total N (TN) and 0.08-0.42 g total P (TP) per day. Raceways were operated approximately 260 days each year (roughly April 1 to Dec 15) from 2003 to 2006. Mean algal productivity values increased from approximately 2.5 g dry weight per square meter per day at the lowest loading rate (0.3 g TN per square meter per day) to 20 g DW per square meter per day at the highest loading rate (2.5 g TN per square meter per day). Mean N and P contents in the dried biomass increased 1.5 to 2.0 -fold with increasing loading rate up to maximums of 7 % N and 1.4 % P. Although highly variable, algal N and P accounted for roughly 50% of input N and P.