What is a reservoir? The Reservoirs Act 1975 (RA 1975), as amended by the Flood and Water Management Act 2010 (FWMA 2010), applies only to 'large raised reservoirs', which includes: • a large raised structure designed or used for collecting and storing water • a large, raised lake or other area capable of storing water which was created or enlarged by artificial means A structure or area is 'raised' if it is capable of holding water above the natural level of any part of the surrounding land (RA 1975, s A1(2)). A raised structure or area is 'large' if it is capable of holding 25,000 cubic metres of water in England or 10,000 cubic metres in Wales above the natural level of any part of the surrounding land. Large raised reservoirs need to be registered with the Environment Agency (EA) in England or Natural Resources Wales (NRW) in Wales. The calculation of capacity of a large raised reservoir is provided in the Reservoirs Act 1975 (Capacity, Registration,