The life histories, abundance, biomass, and production of two species of net-spinning caddisflies, Cheumatopsyche analis and Hydropsyche betteni Ross (Trichoptera: Hydropsychidae), were determined from a 3^rd-order stream in Virginia. These are the only two species of hydropsychid caddisflies occurring in Upham Brook, which flows through a highly urbanized watershed and which is hydrologically altered by a small (4.85-ha) impoundment. Sampling was conducted at least monthly over one year at sites above, immediately below, and 1 km below the impoundment. Both species produced clear winter and spring–early summer generations as well as one or more additional, partial generations later in the summer. The annual mean density and biomass of C. analis were significantly greater (p < 0.05) immediately below the impoundment (2490 individuals/m²; 972 mg/m²) than above (1315 individuals/m²; 360 mg/m²) and 1 km downstream from the impoundment (1466 individuals/m²; 467 mg/m²). Annual production of C. analis was 18.2 g m⁻² yr⁻¹ immediately below the impoundment and 7.2–9.5 g m⁻² yr⁻¹ at the other sites. Mean density and biomass of H. betteni were significantly greater 1 km downstream from the impoundment (156 individuals/m²; 236 mg/m²) compared to above and immediately below the impoundment (28–44 individuals/m²; 13–38 mg/m²). Annual production of H. betteni was highest at 2.5 g m⁻² yr⁻¹ 1 km downstream from the impoundment and 0.3–0.7 g m⁻² yr⁻¹ at the other two sites. The production of both species thus was greatest below the impoundment, but peak production of the two species varied depending on the distance below the dam.