SYNOPSISFollowingPublicationof early proposals for the Reservoirs Act 1975, a systematic programme of reservoir investigation and repair work was carried out by the Department of the Environment for Northern Ireland, Water Service.The paper describes the full procedure followed for data collection, inspections, risk classification and stability and hydraulic investigations of 60 ‘large raised reservoirs’ impounded by dams up to 42 m high and up to 148 years old. Also described are examples of some unusual repair works carried out, and the implementation of a recording, monitoring, and inspection system which now continually oversees all of the reservoirs invol