Because watershed collaborations connect economic and environmental concerns, they are of interest to students of sustainable economic development. The economic outcomes of such collaborations are difficult to study because socio-economic data collection areas do not generally correspond to collaboration boundaries and also because of the simultaneity of economic stimuli and restrictions in collaborative arrangements. This case study of New York City’s Watershed Collaboration in its Catskill Delaware Watershed used a mapping program to create a database of Watershed residents from the 1990 and 2000 census. It provides a heretofore unavailable socioeconomic portrait of the Watershed and trends in indicators relevant to Collaboration effectiveness such as age, demographic pressures, and economic welfare. Through the use of national, state, regional and rural controls, the study also explores the impact of the agreement on the Watershed. Results do not provide evidence of a net negative impact and are consistent with a net positive impact. Several trends which work against agreement effectiveness are identified.