Sarayu was an ancient Indian river, sometimes thought of at probably today's Ghaghara river, and sometimes as a tributary. The river where Lakshamana practices austerities.
The Sarayu (also Sarju) is a river that flows through the Indian states of Uttarakhand and Uttar Pradesh. This river is of ancient significance, finding mentions in the Vedas and the Ramayana. The Sarayu forms at the confluence of the Karnali (or Ghaghara) and Mahakali (or Sharda) in Bahraich District. The Mahakali or Sharda forms the Indian-Nepalese border. Ayodhya is situated on the banks of river Sarayu. Some mapmakers consider the Sarayu to be just a section of the lower Ghaghara River.
On Ram Navami, the festival that celebrates the birthday of Lord Rama, thousands of people take a dip in the Sarayu River at Ayodhya.