Ecosystem metabolism was measured in 10 streams flowing into New York City drinking-water-supply reservoirs. Six of the streams were located west of Hudson River (WOH) in the Catskill Mountains and 4 were in the Croton River watershed east of Hudson River (EOH). Measurements were made for 3-d periods between June and November in each of 3 y using an open-system O₂ technique with reaeration determined from propane evasion. Chlorophyll a concentrations, algal cover types, and nutrient uptake were measured concurrently. Gross primary productivity ranged from 2.02 to 4.32 g O₂ m⁻² d⁻¹ in the WOH streams and from 0.23 to 1.13 g O₂ m⁻² d⁻¹ in the EOH streams. Community respiration ranged from 3.94 to 8.30 g O₂ m⁻² d⁻¹ in the WOH streams and from 1.39 to 6.12 g O₂ m⁻² d⁻¹ in the EOH streams. All streams were heterotrophic. The WOH streams were larger and more open than the EOH streams. Metabolism was strongly correlated with instream environmental and water-chemistry variables and riparian shade. Land use was largely forested with some agriculture in the WOH watersheds, and it was forested or urbanized in EOH watersheds. Landuse impacts were confounded by the smaller size and denser shade along EOH streams than along WOH streams.