The Lee Navigation is a canalised river incorporating the River Lea (also called the 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. The Lee Navigation is named by Acts of Parliament and is so marked on Ordnance Survey maps. Constructed elements and human features are spelled Lee, such as the canal system and Lee Valley Park. The un-canalized river is spelled Lea, along with other natural features such as Lower Lea Valley. More information on the Wikipedia page [1].