This report presents the water-quality data collected during 1998-99 from the land owned by the Prairie Island Indian Community at the northern end of Prairie Island, Minnesota. The data were collected by the U.S. Geological Survey in cooperation with the Prairie Island Indian Community. Seventeen monitoring wells were installed by the U.S. Geological Survey in 1998. Fifteen of the wells were installed with the screen at the water-table. The well screens for the other two wells were approximately 26 and 56 feet below the water table. Samples were collected from the wells in 1998. The water-quality properties and constituents determined for the 17 wells include temperature, pH, specific conductance, dissolved oxygen, alkalinity, major ions, nutrients, and iron and manganese. Water samples collected from two of the wells were analyzed for common agricultural pesticides. In addition, semiquantitative immunoassay screens for presence of atrazine and related triazine herbicides were conducted on samples from all 17 wells. Water-surface altitudes were measured during 1999 in the 17 wells and at 8 surface-water sites.