Canvey Island barriers spanning Benfleet Creek to the north and East Haven Creek in the west. The drainage system consists of sewers, culverts, natural and artificial dykes and lakes which feed seven pumping stations and gravity sluices that discharge the water into the Thames and creeks. Four of the discharge sites are "high flow" stations capable of discharging 600 litres of water per second at any tide level. The levels within the system are managed by a further five "low flow" pumping stations. The Environment Agency's Thames Estuary 2100 flood defence plan includes Canvey Island as one site for alleviating the flood
Tamar–Tavy Estuary Seaweeds, green algae and communities of polychaete worms are all found in the estuary system; near Calstock is found the shrimp "Palaemon longirostris", which has been recorded in only two other estuaries in Britain. The estuary is also one of only two sites in the UK where the fish, allis shad, spawn. Other larger animals found in undisturbed parts of the SSSI include the European otter, the common kingfisher and dormice. Tamar–Tavy Estuary The Tamar–Tavy Estuary is a Site of Special Scientific Interest (SSSI) covering the tidal estuaries of the River Tamar and the River Tavy on the border between