The Day River is a river in Vietnam. It was formerly known as Hát River or Gián Khẩu River. The river is a distributary of the Red River, draining into the Gulf of Tonkin.
The river has a length of 240 km and has a drainage basin of more than 7,500 km2, flowing through Hanoi, and the provinces of Hòa Bình, Hà Nam, Ninh Bình and Nam Định.
Wikipedia https://en.wikipedia.org/wiki/Đáy_River
Coordinates 20°1'1.845" N 106°6'37.438" E
