The river Lee (or Lea) runs from the Thames to Hertford, with a branch along the Stort Navigation. Unlike the other canals in London it was not constructed in one primary phase of building, and also unlike the other canals it is a canalised river, not an entirely new canal. Navigation took place in the first millennium, with the Vikings apparently taking the opportunity to plunder the unfortunate people of Hertford. Work on improving the river's navigability is recorded as early as the fourteenth century and in 1425 there was an Act of Parliament to provide for further improvements. The River lea Commissioners, who used to run it, date back to this period. As was so often the case, where rivers were improved for navigation, there were arguments between barge owners and mill owners who preferred the available water to be used to mills rather than locks. The navigation was much used for carrying grain for beer and bread making and those who might lose their livelihoods from the lower prices that became possible as a result of cheaper transport also objected to improvements. Disputes over the right of navigation reached the Star Chamber, a superior court of justice, in 1594, which ruled in favour of the boats.
The canal era was marked by the passage of the River Lea Act 1766 which authorised much more extensive improvement works and the construction of locks, new sections, and the Limehouse Cut, a connecting canal at the southern end. The locks were, of course, single gate locks which relied on a build-up of water and its sudden release to enable boats to pass. The type of lock we know today is a pound lock, with gates at each end, which is far less wasteful of water. Pound locks were introduced to the river Lea in 1771.
There were substantial improvements in the nineteenth century with a further act being passed in 1850 to authorise new sections and locks. The Lea Conservancy Act 1868 placed the navigation in the hands of a new conservancy board. The twentieth century also saw great improvements, with a major scheme being started in 1922 to enlarge and rebuild locks to enable larger vessels to use the navigation. There was further work carried out in the 1930's to provide for flood relief. On nationalisation of the canal system, the navigation passed to the British Transport Commission and later British Waterways.
Further reading: London's Lea Valley, by Jim Lewis. This is normally in stock in the museum shop or can be ordered from Amazon.co.uk
Order London's Lea Valley: Britain's Best Kept Secret from Amazon.