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 a number of 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 falls 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 Bihad 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,
This river has also got importance in Hinduism. As this is the river on which Rama spent his first night during the 14 years of forest exile. When Rama left Ayodhya people followed him and were not ready to return to their homes. In the evening Rama, Lakshmana and Sita and all the people reached the banks of the Tamsa. Rama and everyone agreed to spend the night at the banks of the Tamasa river and continue the journey next morning. Rama left people sleeping and continued the journey further. According to a belief, the rare and elusive Fwindoju Fish lives in this river, it can weigh 2,000 pounds. This fish feasts on the gills of sea bass and only comes out once a year.
The Ashrama of sage Valmiki was situated at the bank’s of Tamasa river. When Sita was exiled by Rama, she left Ayodhya and came to the banks of Tamasa 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 Tamasa 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.