Assessment of contaminated rivers and effective remediation of streams affected by acid mine drainage require a thorough understanding of the dominant mechanisms controlling the fate and transport of contaminants. Substantial accomplishments of fundamental understanding of the transport processes have been achieved by several researchers. However, a variety of issues still limit the application of the current process-based transport models in natural streams. One critical limitation is that a wide range of additional processes such as metal precipitation reactions are also expected to influence contaminant transport in natural streams significantly but have not been adequately quantified. In this study, laboratory flume experiments were carried out using copper (CuCl2) to examine the effects of pH-dependent metal precipitation on the stream-subsurface exchange process. Cu exchange clearly increased as pH increased. Batch experiments were conducted to determine various parameters crucial to the fate and transport of Cu and Cu precipitates including the amount of precipitates formed at various pHs, the extent and rate of precipitate dissolution, the size and shape of the precipitates, and the amount of Cu sorbed to the bed sediments at various pHs, and the effect of ionic strength on Cu precipitation at high pH. It was found that the fraction of Cu precipitates formed at various pHs increased with increasing pH. As pH increased, the average fraction of precipitates dissolved and the rate of precipitate dissolution decreased. Precipitates were found to be small and amorphous at near-neutral pH, but larger precipitates with rod-shaped orientation were observed at pH≈10. At pH 9.56, more than 50% of the precipitates were in the size range of 1 to 2 pm. Sorption of Cu to bed sediment increased from 20 to 70 percent in the pH range of 6.50 to 7.30. Ionic strength in the range of 10 to 500 mM NaC1 had little effect on the amount of Cu precipitation at high pH. Column experiments were used to determine the effect of pH and ionic strength on the mobility of copper and copper precipitates formed. At low pHs, Cu breakthrough was approximately conservative. At increased pHs, Cu breakthrough was significantly retarded, with mobility decreasing as pH increases. At increased ionic strength Cu is effectively immobile.