A procedure is described for conducting an aquatic hazard assessment of selenium. Hazard is characterized in terms of the potential for food-chain bioaccumulation and reproductive impairment in fish and aquatic birds, which are the most sensitive biological responses for estimating ecosystem-level impacts of selenium contamination. Five degrees of hazard are possible depending on the expected environmental concentrations of selenium, exposure of fish and aquatic birds to toxic concentrations, and resultant potential for reproductive impairment. The degree of hazard is given a numerical score: 5, high hazard; 4, moderate hazard; 3, low hazard; 2, minimal hazard; and 1, no identifiable hazard. A separate hazard score is given to each of five ecosystem components: water, sediments, benthic macroinvertebrates, fish eggs, and aquatic bird eggs. A final hazard characterization is determined by adding individual scores and comparing the total to the following evaluation criteria: 5, no hazard; 6-8, minimal hazard; 9-11, low hazard; 12-15, moderate hazard; 16-25, high hazard. An example is given to illustrate how the protocol is applied to selenium data from a typical contaminant monitoring program.