An environmental monitoring study was carried out between 1993, 1995 on the site of a marine trout farm located in the Bay of Cherbourg (English Channel), France. The study dealt with the sea bottom and solid waste from the farm, and concerns the deposition rate, sediment analysis and chemistry (fine fraction < 63 μm, organic matter, carbon, nitrogen and trace metals such as Cu and Zn), bottom oxygen demand, benthic macrofauna, and underwater video surveying. The observed impact was very moderate and localised, and showed no real abnormality. This was mainly due to the strong hydrodynamics characterising the site. A separate phase of the same study dealt with dissolved waste and the water mass (Part One: Current and water quality).