From the Wikipedia page [1]
The Pool of London is a part of the Tideway of the River Thames from London Bridge to below Tower Bridge. It was the original part of the Port of London. The Pool of London is divided into two parts, the Upper Pool and Lower Pool. The Upper Pool consists of the section between London Bridge and Tower Bridge, while the Lower Pool traditionally runs from Tower Bridge to the Cherry Garden Pier in Rotherhithe.
The Hidden London page is here.