The effectiveness of mechanical removal of substrates for the control of benthic chironomid midge populations in a concrete-lined flood control channel system (draining domestic and industrial waste water and storm water) was studied. Substrates from a 0.80 km long section of one of the channels were mechanically removed. Fine sand and detritus were the 2 predominant types of substrates in the area cleared. Preand post-removal benthic samples were taken at 3 sites in the area cleared of substrates. One site, serving as check, was located upstream in the uncleared area.Midge larvae and pupae belonging to 5 genera were taken. In pre-removal samples taken from the area cleared of substrates, larvae ofCricotopusspp. andDicrotendipessp. predominated and formed 89.1% of the total midge fauna. Pupae constituted 10.1% of the total immature midges. The average midge density in the area cleared of substrates was 1303/0.09 m2prior to the removal of substrates. Samples collected 3 days after removal showed a reduction of 87.0% in the total midge fauna. Satisfactory midge control lasted for 2 weeks. Benthic midge populations recovered completely after 4 weeks.