The uranium concentration and isotopic composition of water and suspended sediment from a South Texas river and estuary were determined by alpha-spectroscopy. The average dissolved uranium concentration and radioactivity ratio (U²³⁴/U²³⁸) of the river water were determined to be 2.44 ug/l and 1.15, respectively. Water from a tributary of the river was found to contain an average dissolved uranium concentration of 42.8 ug/l with an isotopic radioactivity ratio of 1.56. Close inspection of the lateral concentration and isotopic activity ratio of uranium revealed an increase below the confluence of a tributary and the river. A model was derived based on equations used in isotopic dilution analysis, which predicts these increases within analytical error. This model may be useful in future studies to locate extraneous uranium within the hydrologic environment.

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