A water intake and pretreatment system (10) comprising an inlet for delivering water from a natural source to a reservoir (12)； said inlet to reservoir having a net screen (16) to prevent entry of organisms above a predetermined size and including a one- way gate (30) to allow organisms to exit the reservoir； said reservoir further comprising a granular filter media for water and algae filtration； and a drainage layer for removal of filtered water from the granular filter media to a drainage outlet. A local backwashing apparatus (40) is included for localized backwashing of the granular filter media.
