The River Lea at 7 am today.
The Lea rises somewhere north of Luton and eventually flows into the Thames at London. It gives its name to Luton, which means "Settlement on the Lea". The name Lea is thought to be Celtic, like a number of English river names, and mean something like "Bright" or "Shining".
I think it is from the same Indo-European root as "light", which seems to be cognate with Latin lux "light", Greek lefkos "white", German licht, Gaelic solas "light" (in the physical sense), Welsh lleuad "moon".