|State||Madhya Pradesh, Uttar Pradesh|
|• location||Maihar tehsil, Satna district, Kaimur Range, Madhya Pradesh|
|• elevation||610 m (2,000 ft)|
|Prayagraj, Uttar Pradesh|
|Length||264 km (164 mi)|
|Basin size||16,860 km2 (6,510 sq mi)|
The Tamsa River (also called as Tons river) is a tributary of the Ganges flowing through the Indian states of Madhya Pradesh and Uttar Pradesh.
The Tamsa rises in a tank at Tamakund in the Kaimur Range at an elevation of 610 metres (2,000 ft). It flows through the fertile districts of Satna and Rewa. At the edge of the Purwa plateau, the Tamsa and its tributaries form many waterfalls. The river receives the Belan in UP and joins the Ganges at Sirsa, about 311 kilometres (193 mi) downstream of the confluence of the Ganges and Yamuna. The total length of the river is 264 kilometres (164 mi). It has a total drainage area of 16,860 square kilometres (6,510 sq mi).
The Tamsa River while descending through the Rewa Plateau and draining northwards makes a vertical fall of 70m known as Purwa Falls. Some of the more notable waterfalls on the tributaries of the Tamsa river, as they come down from the Rewa Plateau, are: Chachai Falls (127m) on the Beehar River, a tributary of the Tamsa, the Keoti Falls (98m) on the Mahana River, a tributary of the Tamsa, and Odda Falls (145m) on the Odda River, a tributary of the Belah River, which is itself a tributary of the Tamsa, Actually, the Tamsa River described in Valmiki Ramayana is a seasonal rivulet, originates somewhere in Barabanki, and flows through the Ayodhya district to Darban lake in Tanda tehsil in Ambedkar Nagar. This river is left side of Ganga and Gomti. Thus has no relation to Reva or Madhya Pradesh.
This river has also got importance in Hinduism. As this is the river on which Shri Rama spent his first night during the 14 years of forest exile. When Shri Rama left Ayodhya people followed him and were not ready to return to their homes. In the evening Shri Rama, Lakshmana and Sita and all the people reached the banks of the Tamsa. Shri Rama and everyone agreed to spend the night at the banks of the Tamsa river and continue the journey next morning. Shri Rama left people sleeping and continued the journey further.)
The Ashrama of sage Valmiki was at the banks of Tamsa river. When Mata Sita was exiled by Shri Rama, she left Ayodhya and came to the banks of Tamsa river some 15 km away from the city, where she met Valmiki. He requested Sita to live in his ashrama situated at the bank of the Tamsa river. Here Sita spent all her remaining life, and here her twin sons Lava and Kusha received education and trained in military skills under the tutelage of Valmiki.
Also on the banks of river Tamsa was the ashram of Bharadwaj, mentioned in the Valmiki Ramayana; it is here that on seeing the plight a bird couple, Valmiki created his first verse, shloka.