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Three Mills Lock, also known as the Prescott Lock is on the Prescott Channel on the River Lea in London. The project was led by British Waterways and the lock officially opened on 5 June 2009.
The lock cuts off this section of the Bow Back Rivers from the tide, creating new opportunities for leisure boats, water taxis, trip boats and floating restaurants. It also helps freight traffic such as barges carrying construction materials to the sites of the 2012 Olympics and Stratford City.
Wikipedia: Link

The Lee Navigation is a canalised river incorporating the River Lea (River Lee). It runs from Hertford Castle Weir to the River Thames at Bow Creek; its first lock is Hertford Lock and its last Bow Locks.
See Wikipedia article: Link