Built in 1801, the Blackwall Basin was the first impounded dock entrance basin ever built. In effect it was a big entrance lock. Ships could be locked into it at high tide and then lock into the docks when they wanted without affecting the water level in the docks. Its banks have been altered, but it still remains close to its original shape. Apart from the addition of some jetties it has had little change. This area is in the area called Poplar, which takes its name from the Black Poplar trees which once flourished in the marshy area that existed here before 1800. Black Poplar is a very rare and exceptionally large tree that grows well in the wet conditions which the Thames and Lea historically brought to much of the neighbourhood.