During July 1979, ~345 tonnes of crushed limestone were placed in the bed of a small, seasonally acidic stream. Addition of the limestone resulted in substantial alteration of water chemistry including significant elevations in pH, alkalinity, conductivity, Ca and Mg. During a one year period, contributions of buffering to the stream from the limestone were substantial with loading estimates indicating a decrease of ~65% (~3100 g) in. H+ and an increase of ~145% (9000 kg) in alkalinity as CaCO3. Neutralization by the limestone was sufficient to protect incubating rainbow trout eggs during a period of moderate flow in late spring. However, during a previous period of very high flow, low pH and almost complete mortality of brook trout eggs were observed downstream of the limestone. No influence by the limestone application on natural fish and macroinvertebrate communities or on introduced brook trout fingerlings was apparent.