The River Lea (sometimes called the River Lee, and once the Ley, but that's another story) rises near Luton and runs south, reaching London near [Waltham Abbey]?, then proceeding through northeast and east London (giving Leyton its name on the way) to flow into the River Thames at [Blackwall]?. For much of its metropolitan course, the Lea is accompanied by the Lee Navigation, a canal built alongside the river to assist navigation, thus making the Lea the world's first dual-carriageway river.
The area around the river is called the [Lea Valley]?, although it's not much of a valley.
I love the Lea. I'll write more about it when i have more time. -- Tom A