The Évançon (sometimes written Évençon) is the stream which flows through the val d'Ayas and flows into the Doire baltée. Its name in Franco-Provençal might mean "Grand River" or "River from the Mountaintops" (eva d'en som). In archival documents it is often referred to as l'eau blanche (French for "Whitewater").The Unité des communes valdôtaines de l'Évançon takes its name from the stream.