AbstractA Royal Commission report in 1872 revealed that the Clyde was one of the most heavily polluted rivers in Britain. Despite notable efforts to reduce pollution after the Rivers Pollution Prevention Act, 1876, little real improvement took place, and the quality of the river actually worsened during the first half of the present century. The Clyde River Purification Board, established in 1956, has taken almost 30 years to restore the river to its present state of health, with salmon once again returning to spawn after an absence of over 120 years. The author examines the reasons for this long delay and considers whether present controls are adequate to meet the needs of the future in the face of rapidly changing industrial effluents.