The Port of London Authority (PLA) is a self-funding public trust established by The Port of London Act 1908 to govern the Port of London. Its responsibility extends over the Tideway of the River Thames and its continuation (the Kent/Essex strait). It maintains and supervises navigation, and protects the river's environment. The PLA originally operated all enclosed dock systems on the river (except the Regent's Canal Dock), but these have long been closed to commercial traffic, with the exception of Port of Tilbury, which was privatised in 1992.