Table 1. Grand mean (data from several stations) (+1 sem) of trace metal concentrations (mg/g) in caddisfly larvae (Hydropsyche spp.) collected in 19& in the Clark Fork River upstream or the confluence or the Little Blackfoot River (0-60 km), between the confluences or Flint Creek and Rock Creek (101 164 km), and between the confluences or the Blackfoot and Flathead River (191-381 km) compared to metal concentrations or specimens from tributaries Tributary concentrations are for samples (number of stations shown in parentheses) from the Little Blackfoot River, Rock Creek, and the Blackfoot River.