The watershed and estuary of Waquoit Bay, Massachusetts, U.S.A was analysed from 1938-1990 evaluating the change in nitrogen levels due to atmospheric conditions, use of fertilizer, and wastewater. Due to an increase in urbanization the overall trend was a decrease in the percentage of nitrogen from atmospheric deposition, a small increase in the percentage due to fertilizer use, and a significant increase in the percentage of nitrogen due to wastewater disposal. In 1938 95% of the nitrogen load entering the watershed was from atmospheric deposition, 3% was from fertilizers, and 2% was from wastewater. In 1990 only 59% of the nitrogen entering the watershed was from atmospheric deposition, 19% was due to fertilizers, and 22% was now due to