We measured the impacts of beaver impoundments on the water chemistry of two headwater streams on the Appalachian Plateau, an unnamed tributary to Herrington Creek (HR), and Mountain Run (MT). We measured acid-neutralizing capacity (ANC), pH, conductivity, discharge, temperature, and the concentrations of major ions, dissolved organic carbon (DOC), and trace metals in stream water upstream and 1 m, 10 m, and 100 m downstream of the beaver impoundments and at two locations, 147 m apart, in a tributary to HR that did not contain a beaver impoundment. There were significant differences in water chemistry upstream and downstream of the beaver impoundments at both MT and HR, but these differences were generally confined to the summer. During the summer, both beaver impoundments generated ANC and increased pH by acting as sinks for NO₃ and sources of NH₄⁺, iron, and manganese. In addition, the beaver impoundment at MT was a sink for SO₄² and the impoundment at HR was a source of DOC. The generation of ANC by beaver impoundments may be important to streams of this region where inputs of strong acids from atmospheric deposition are relatively high.