| Lay | |
| Map: | Lay (fleuve).png |
| Source1 Location: | Saint-Pierre-du-Chemin |
| Source1 Coordinates: | 46.7094°N -0.7103°W |
| Mouth Location: | Bay of Biscay |
| Mouth Coordinates: | 46.3206°N -1.3028°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | France |
| Length: | 120km (80miles) |
| Source1 Elevation: | 195m (640feet) |
| Mouth Elevation: | 0m (00feet) |
| Discharge1 Avg: | 14m3/s |
| Basin Size: | 1750km2 |
The Lay (pronounced as /fr/) is a 120km (80miles) river in the Vendée département, western France. Its source is at Saint-Pierre-du-Chemin and it flows generally southwest. It flows into the Bay of Biscay between La Faute-sur-Mer and L'Aiguillon-sur-Mer, 20km (10miles) northwest of La Rochelle.
Its main tributaries are the Yon and the Smagne.
This list is ordered from source to mouth: