AbstractUranium mining is an important industry in the Rocky Mountain region; however, little is known about the environmental hazards of uranium to fish and other aquatic organisms.Indian Creek, a hard‐water stream (200 mg/L as CaCO3) near Gunnison, Colorado, receives periodic discharges of runoff from a uranium mine. In addition, natural springs contribute uranium to the creek. As a result, uranium concentrations in the creek range up to 4 mg/L, concentrations which are potentially toxic to trout based on published toxicity data. Therefore, we conducted a series of studies to analyze the potential toxicity and bioaccumulation of uranium in Indian Creek and downstream waters.A 60‐d post‐hatch, early life stage toxicity test was conducted with brook trout in water of hardness and alkalinity similar to Indian Creek. Additional tests were performed in soft and hard water (96‐h acute toxicity tests) and in water of Indian Creek's quality (48‐h acute toxicity tests). Trout from the 60‐d test were also analyzed for uranium bioaccumulation. To confirm the results of the laboratory studies, these data were compared with on‐site field study data, including surveys of fish and benthic invertebrates, and analyses of uranium levels in trout. The laboratory results indicated that the high hardness and alkalinity of the test water greatly reduced the potential toxicity of uranium to trout. Concentrations estimated to be chronically toxic from the early life stage test were greater than 9 mg/L; whereas the 48‐h LC50was 59 mg/L. Bioconcentration factors for uranium were low, ranging from 1.9 to 4.3.Benthic invertebrate and fish studies conducted in Indian Creek confirmed that current uranium concentrations are not significantly toxic to resident aquatic biota. In‐stream bioaccumulation of uranium is also very low, and is comparable to the laboratory‐derived values.Our study demonstrated that laboratory toxicity and bioaccumulation tests can accurately evaluate potential in‐stream hazards of uranium. To accurately estimate in‐stream toxicity and bioaccumulation of metals, it is important that laboratory tests simulate
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