The Kolong River is a tributary of the Brahmaputra River, which diverts out from the Brahamputra river in Hatimura region of Jakhalabandha (Nagaon district, Assam, India), and meets the same at Kolongpar near Guwahati. The tributary is about 250 kilometres (160 mi) long and flows through the districts of Nagaon, Morigaon and Kamrup; on the way, several smaller streams (Diju, Misa and others) meet it. The river flows through the heart of the Nagaon urban area dividing the town into Nagaon and Haiborgaon.
Not much is known about the pre-colonial period of the river. In the colonial period, though, the river was known to be widely used for passenger and goods transport, specially because the road and rail network was undeveloped or underdeveloped during that period. That is why the British colonial administration almost established the district headquarters in Puranigudam, on the bank of the river.
Until the colonial period, the Kolong river and smaller streams feeding the river were the main sources of potable water. Most of the villages were settled on their banks. People became heartily attached to the river, and as one folk tale says, it was just "Kolong" for them, they refused to say it was even a river.
In those days, the river created havoc by flooding the lowland areas in the present Nagaon and Morigaon districts during the rainy season, as it received water not only from the smaller streams, but also from the overflowing Brahamaputra. Sometime in the 1960s, a major flood caused a threat to existence of the Nagaon town itself, which lies in a lowland area. The mouth of the river in Hatimura region of Jakhalabandha was permanently closed subsequently, allowing the river to carry the water only from the smaller streams to Brahamaputra. Following this, the threat of flood disappeared. However, due to lack of enough water, especially during the dry winter, the river dried almost halfway. In several places, the river presently looks like a closed pond, covered with water hyacinth. Due to the lack of current, many sand-sores were formed in and around the river. The population of flora and fauna also diminished on the river and several other water bodies.
Numerous fictional and non-fictional, famous and not-so-famous articles, and poems have been written taking the river as a main subject or character. The lamous Assamese poet, the late Nabakanta Baruah Nabakanta Barua wrote a famous novel Kokadeutar Had: The Bone of (my) Grandfather, fictionalizing the river and its history.