Water-quality samples were collected from the Upper Delaware Scenic and Recreational River (UPDE) and its tributaries during the period October 1, 2005, to September 30, 2007, to document existing water quality, determine relations between land use and water quality, and identify areas of water-quality concern. A tiered water-quality monitoring framework was used, with the tiers consisting of intensively sampled sites, gradient sites representing the range of land uses present in the basin, and regional stream-survey sites. Median nitrate and total phosphorous concentrations were 1.15 and 0.01 mg/L (milligrams per liter) for three sites on the mainstem Delaware River, 1.27 and 0.009 mg/L for the East Branch Delaware River, 2.04 and 0.01 mg/L for the West Branch Delaware River, and 0.68 and 0.006 mg/L for eight tributaries that represent the range of land uses resent in the basin, respectively. The percentage of agricultural land varied by basin from 0 to 30 percent and the percentage of suburbanization varied from 0 to 17 percent. There was a positive correlation between the percentage of agricultural land use in a basin and observed concentrations of acid neutralizing capacity, calcium, potassium, nitrate, and total dissolved nitrogen, whereas no correlation between the percentage of suburbanization and water quality was detected. Results of stream surveys showed that nitrate concentrations in 55 to 65 percent of the UPDE Basin exceeded the nitrate reference condition and a suggested water-quality guideline for ecological impairment in New York State (0.98 mg/L) during the spring. Many of the affected parts of the basin were more than 90 percent forested and showed signs of episodic acidification, indicating that the long-term effects of acid deposition play a role in the high nitrate levels. Nitrate concentrations in 75 percent of samples collected from agricultural sites exceeded the suggested nitrate water-quality guideline for ecological impairment. Concentrations of nitrate and total phosphorous in samples collected from agricultural sites also were twice and 25 percent higher than those in samples from reference sites, respectively.