Teddington Lock is a complex of three locks and a weir on the River Thames between Ham and Teddington in the London Borough of Richmond upon Thames, England. Historically in Middlesex, it was first built in 1810. The limit of legal powers between the Port of London Authority, the navigation authority downstream to the North Sea and that upstream to small headwaters of the river, the Environment Agency, is marked nearby by an obelisk on the "Surrey" (towpath, right) bank. The weir named Teddington Weir marks the river's usual tidal limit and is the lowest on the Thames. This lock is the lowest full-tide lock and second lowest of all-tide locks on the Thames. The complex of civil engineering or infrastructure in essence consists of a large long weir and three locks: a conventional launch lock in regular use, very large barge lock and a small skiff lock. The barge lock was made to accommodate long barges, steamers or passenger ferries and has an additional set of gates half-way to operate more quickly for shorter craft. The staggered structures incorporate two reinforced narrow islands. The upper island is traversed by and accessible by the lock gates or Teddington Lock Footbridge. Location and design The greater lock is against the general south (right, towpath or Surrey) bank of the river which is for 500 m north-east here; a middle lock being that most regularly used spans a long thin island which has lawns, places for boat owners to sit and a lock keeper's cabin and short thin island which is a thin wedge of concrete and a broad canoe/kayak stepped portage facility. The river downstream of the lock is the Richmond and Twickenham reach of the Tideway, a reach of semi-tidal river due to the fact the Richmond Lock and half-tide barrages limits the fall of water thereby maintaining a head of water to aid navigability at and around low tide. Though the weir at Teddington Weir marks the managed river's usual tidal limit, after prolonged rainfall causing very high fluvial flow, specifically at high tide, a higher limit of slack water (stand of the tide) causes eddies to arise as far upstream as the top of this reach, the next lock. The large, bow-shaped Teddington Weir is against the opposite bank. A series of two footbridges at differing heights make up a structure which crosses the locks, the middle island