This chapter compares habitat use by juvenile salmon, Salmo salar L. and trout, S. trutta L., in a chalk stream in southern England and the effects of shading and flow control on population density and mortality.Salmon tended to occupy water between 25 and 55 cm deep with a velocity between 0.4 and 1.0 m s −1 . First year salmon were associated with gravel substrates during the daytime and aquatic weed at night, and occupied shallower and slower habitats at night in the autumn. Trout were associated with a greater range of habitats than salmon, generally occupying deeper and faster water with increasing age. First year trout were found along the shallow (5-10 cm) and slow flowing (−0.1 to 0.4 m s −1 ) margins of the stream among tree roots and on silty substrates.First year salmon and trout subject to low summer flow showed no net downstream displacement. However, an increase in mortality rate was apparent for both species.There appeared to be positive effects of canopy removal on the availability of potential prey for juvenile salmonids. First year salmon and trout had lower densities under closed canopy with little in-stream weed, relative to adjacent open sites with substantial weed cover.The results suggest that salmon and trout have differing needs that should be elucidated and considered when managing water flow and riparian and in-stream habitat, particularly in chalk streams where salmonid production is failing. In particular, the preference of first year salmon for aquatic weed at night and of 0+ group trout for the cover afforded by the stream margins suggest that excessive cutting of 242 Salmonid Fisheries: Freshwater Habitat Management Paul Kemp