Freshwater (Selenastrum capricornutum) and estuarine (Skeketonema costatum) algae were exposed to liquid wastes from 10 industrial sites in laboratory bioassays. All wastes affected algal growth either by stimulation or by stimulation at low concentrations and inhibition at high concentrations. Generally S. capricornutum and Sk. costatum responded similarly to each waste: SC20's were between 0.01% waste; EC50's, between 5.1% and 85.5% waste. Toxicity to S. capricornutum was lost by the ninth day of exposure in all wastes except one, and it is recommended that algal tests be carried out for four days. Both algal species were more sensitive to the wastes than were Daphnia magna (freshwater) and Mysidopsis bahia (estuarine). Only three wastes were toxic to D. magna and two were toxic to D. magna and two were toxic to M. bahia. SC20 and EC50 values are used to calculate the 7-day, 10-year flow rate required for dilution of effluents to non-toxic concentrations.