This dataset contains water-quality data for stream samples collected by the U.S. Geological Survey at 12 sites on the Assabet and Concord Rivers in eastern Massachusetts in 2008. The samples were collected monthly from June to October, 2008. The water-quality parameters and constituents include field parameters (water temperature, specific conductance, pH, and dissolved oxygen), concentrations of dissolved and total calcium, magnesium, and selected metals, total suspended solids, and dissolved organic carbon. Hardness calculated from dissolved calcium and magnesium also is included. Data collection was done in cooperation with the Massachusetts Department of Environmental Protection and the U.S. Environmental Protection Agency.