| Đáy River | |
| Source1 Location: | Geladaindong Peak, Tanggula Mountains, Qinghai (Đan Phượng) |
| Mouth Location: | Kim Sơn |
| Mouth Coordinates: | 19.9131°N 106.095°W |
| Subdivision Type1: | Country |
| Subdivision Type2: | Region |
| Length: | 240km (150miles) |
| Source1 Elevation: | 5042m (16,542feet) |
| Mouth Elevation: | 0m (00feet) |
The Day River (vi|Sông Đáy) is a river in Vietnam. It was formerly known as Hát River (Vietnamese: Sông Hát or Vietnamese: Hát Giang) or Gián Khẩu River (Vietnamese: Sông Gián Khẩu). The river is a distributary of the Red River, draining into the Gulf of Tonkin.
The river has a length of 240 km[1] and has a drainage basin of more than 7,500 km2,[2] flowing through Hanoi, and the provinces of Hòa Bình, Hà Nam, Ninh Bình and Nam Định.