| Lac de Coiselet | |
| Location: | Ain/Jura |
| Coords: | 46.3278°N 5.6167°W |
| Type: | reservoir |
| Inflow: | Ain, Bienne |
| Outflow: | Ain |
| Pushpin Map: | France Ain |
| Basin Countries: | France |
| Length: | 6km (04miles) |
| Area: | 3.8km2 |
| Depth: | 9.5m (31.2feet) |
| Max-Depth: | 30m (100feet) |
Lac de Coiselet (in French pronounced as /lak də kwazlɛ/) is a reservoir on the border between the Ain and Jura departments in France. Its surface area is 3.8 km2. The lake formed in 1970 after the Barrage de Coiselet was built at the confluence of the rivers Ain and Bienne.