Port of London Authority
The Port of London Authority (PLA) is a self-funding public trust established on 31 March 1909 in accordance with 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. It maintains and supervises navigation, and protects the river's environment.

The Port of London Authority (PLA) is a self-funding public trust established on 31 March 1909 in accordance with 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. It maintains and supervises navigation, and protects the river's environment.
Check the official site before travelling; hours and prices can change.
More bridges

Tower Bridge
The bridge people mean when they say London Bridge. Walk the high-level walkway for the glass floor.

Millennium Bridge
Foot-only suspension bridge from St Paul's to Tate Modern — the only crossing aligned on St Paul's dome.

Hammersmith Bridge
Currently pedestrian-only, Victorian wrought-iron beauty — best photographed at golden hour.
Source: wiki-list