Nutrient, suspended sediment, and pesticide data from 1990 through 2004 in the Red River of the North Basin were compiled, summarized, and compared to historical data. Streamflow varied widely throughout the basin during the 1990-2004 study period. For 19 of 22 streamflow sites, median annual streamflow during the study period exceeded the long-term average streamflow. High streamflow can have a substantial effect on water quality. In water samples from selected surface-water sites, nitrite plus nitrate concentrations ranged from less than 0.005 to 7.7 milligrams per liter; total Kjeldahl nitrogen concentrations ranged from 0.1 to 7.5 milligrams per liter; total phosphorus concentrations ranged from less than 0.005 to 4.14 milligrams per liter; and dissolved phosphorus concentrations ranged from 0.003 to 4.13 milligrams per liter. Surface-water samples from the Pembina River basin generally had higher nitrite plus nitrate, total phosphorus, and suspended sediment concentrations compared to samples from other Red River Basin sites. Historical data from 1970 through 1990 showed relatively high nitrite plus nitrate and suspended sediment concentrations in samples from some Pembina River sites; in contrast to the 1990-2004 period, total phosphorus concentrations from the 1970-90 period generally were highest at Red River of the North sites. Nitrate concentrations in ground-water samples for the 1990-2004 period were highest in Sheridan County, North Dakota and Marshall and Otter Tail Counties in Minnesota. Concentrations of nitrate in ground water in Marshall and Otter Tail Counties corresponded to relatively high reported fertilizer applications during 2002; however, Sheridan County did not have the high fertilizer applications in 2002 compared to other North Dakota and Minnesota counties. The most frequently detected pesticides or pesticide metabolites were 2, 4-D, bentazon, de-ethylatrazine, metolachlor, picloram, and triallate in surface water and alachlor ethanesulfonic acid (ESA), atrazine, de-ethylatrazine, picloram, and triazine in ground water. None of the most frequently detected pesticides or metabolites sampled and analyzed by the U.S. Geological Survey or available in the U.S. Environmental Protection Agency Storage and Retrieval System (STORET) during 1990-2004 were detected frequently during 1970-90, with the exception of 2,4-D.