(1)No large raised reservoir shall be altered in order to render it incapable of holding more than 25,000 cubic metres of water above the natural level of any part of the land adjoining the reservoir, unless a qualified civil engineer is employed to design or approve and to supervise the alteration.
(2)An engineer employed for the purposes of subsection (1) above shall give a certificate, as soon as he is satisfied it is so, that the alteration has been completed and has been efficiently executed.
(3)Where a certificate is given under subsection (2) above, a local authority on receipt of the certificate or a copy of it shall remove the reservoir from their register of large raised reservoirs; but a reservoir that has been a large raised reservoir but is altered so as no longer to be capable of holding more than 25,000 cubic metres of water above the natural level of any part of the land adjoining the reservoir shall nevertheless continue for purposes of this Act to be a large raised reservoir, unless the alteration is made and a certificate given in accordance with this section.