Data on radionuclide concentrations in water and sediment material in the phosphate-mining area of the upper Blackfoot River basin were collected from May to October 1979. Maximum measured uranium and radium-226 concentrations dissolved in water were 3.7 micrograms per liter and 1.8 picocuries per liter , respectively. Maximum measured uranium and radium-226 concentrations in stream-bottom material were 5.5 micrograms per gram and 1.8 picocuries per gram, respectively. Maximum measured uranium and radium-226 concentrations on bottom material were 9.9 micrograms per gram and 3.9 picocuries per gram, respectively, in sediment-retention ponds, and 17 micrograms per gram and 3.5 picocuries per gram, respectively, in a mine pit. Maximum observed radon-222 concentration was 120 picocuries per liter in surface water and averaged 550 picocuries per liter at Formation Springs (site 10). All radionuclide concentrations were within existing State and Federal water-quality standards. Radionuclide concentrations were not significantly increased downstream from active mining sites. (USGS)