 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.