It flows to the Ría de Arosa estuary near the city of Catoira, Spain.

The river is also valued by archaeologists owing to the large number of artifacts, dating as far back as the Neolithic, discovered here.

The outlet of the Ulla River and the mouth of the estuary, called Ría de Arousa, are the two sites where archaeologists have discovered remains consistently.

According to E. Bascuas, "Ulla" is a form belonging to the old European hydronymy, and derived from the Indoeuropean root *wel- 'wheel, rotate'.

This toponym is registered in 906 as "(fluvius) Volia", which had derived from a previous form *Wulia.