| Cosău | |
| Pushpin Map: | Romania |
| Subdivision Type1: | Country |
| Subdivision Name1: | Romania |
| Subdivision Type2: | Counties |
| Subdivision Name2: | Maramureș County |
| Subdivision Type3: | Villages |
| Subdivision Name3: | Budești, Călinești, Cornești, Ferești |
| Length: | 25km (16miles) |
| Mouth: | Mara |
| Mouth Location: | Ferești |
| Mouth Coordinates: | 47.8434°N 23.9367°W |
| Progression: | Mara→ |
| Basin Size: | 116km2 |
| Tributaries Left: | Sâva, Oanța, Râușor |
| Tributaries Right: | Valea Popii |
The Cosău (Hungarian: Kaszó) is a right tributary of the river Mara in Romania. It discharges into the Mara near Ferești.[1] Its length is 25km (16miles) and its basin size is 116km2.[2]