The Thames Estuary is where the River Thames meets the waters of the North Sea, in the south-east of Great Britain. Limits An estuary can be defined according to different criteria (e.g. tidal, geographical, navigational or in terms of salinity). For this reason the limits of the Thames Estuary have been defined differently at different times and for different purposes. Western This limit of the estuary has been defined in two main ways: The narrow estuary is strongly tidal and is known as the Tideway. It starts in south-west London at Teddington Lock and weir, Teddington/Ham. This point is also mid-way between Richmond Lock which only keeps back a few miles of man-made head (stasis) of water during low tide and the extreme modern-era head at Thames Ditton Island on Kingston reach where slack water occurs at maximal high tide in times of rainfall-caused flooded banks. In terms of salinity the transition from freshwater to estuarine occurs around Battersea; east of the Thames Barrier the water is of notable brackishness where fish, particularly in dry summers on the flood (the incoming) tide, are estuarine. The head of Sea Reachthe Kent / Essex Straitsouth of Canvey Island on the northern (Essex) shore. This reach and all more eastern zones (a mixture of channels and shoals) have a width that contributes to the large, archetypal, internal but mainly submerged sandbanks. These come from a combination of silt-borne fluvial and tidal scouring and deposition (silting). Eastern The transition between the Thames Estuary and the North Sea has been located at various notional boundaries, including: The Yantlet Line between the Crow Stone (London Stone) on the northern foreshore at Chalkwell, Westcliffe-on-Sea and another London Stone off the Isle of Grain, to the south. (This marked the seaward limit of the river jurisdiction successively of the City of London and the Thames Conservancy). A line between Havengore Creek, Essex (to the north), and Warden Point, east Sheppey, Kent (to the south), tallying with the easternmost hazardous point of the Nore sandbank. (This formed the seaward limit of the Port of London Authority on its establishment in 1908). A line between North Foreland, Margate, Kent via the Kentish Knock lighthouse to Harwich in Essex. Here begin sandbanks of the bight of this shallow sea. Per a Hydrological Survey of 1882–9. (This tallies with the eastern edge of the current seaward limit of the Port of London