Karatoya River an intriguing river, formerly the main channel of the tista, and perhaps a distributary of the brahmaputra. In the Siyar-al-Mutakhkhirin it is recorded that this river was three times the size of the ganges when bakhtiyar khalji invaded the Northern Region (1115 AD). Tectonic disturbances had broken it up into four distinct parts. The northern part, called the Dinajpur-Karatoya, is the main source of the atrai. It rises in a marsh in Baikanthapur in Jalpaiguri (India), but also receives water from underground streams. In khansama upazila its name changes to Atrai. The Dinajpur-Karatoya was connected with the Rangpur-Karatoya north of Khansama, but very little water now passes down that channel. The upper part of Rangpur-Karatoya originates in the Jalpaiguri district of India and is known as the Deonai-Jamuneshwari up to gobindaganj upazila.
The Jamuneshwari-Karatoya flows in slight meanders south-southeast to Gobindaganj upazila where the main stream turns east through the Katakhali and falls into the bangali. The portion of the former river passing through shibganj upazila is dry most of the year. It effectively separates the Rangpur-Karatoya from the Bogra-Karatoya. The latter river flows south past bogra town till it joins the Bangali to make Phuljhor river, which falls into the hurasagar. The maximum discharge of the Bogra-Karatoya is below 3,000 cusec and has declined rapidly since the construction of the Brahmaputra Right Embankment. The fourth part, the Pabna-Karatoya, is a moribund riverbed near Handial. Various other channels are also pointed out as parts of the Old Karatoya.
The ancient Karatoya must have been a large river. In Ven den Brouck's map of Bengal, prepared in 1660, it is shown as a large channel, and in the map of rennell, prepared in 1776, it is still a major river. As late as 1810, Buchanan-Hamilton writes of it as 'a very considerable river'. The decline however, came so rapidly after the 1820 flood that the old banks of the river are distinctly traceable. The river was formerly sacred to the Hindus, as the derivation of the name shows. Kar (hand) and Toa (water) signified that the river was formed by the water which was poured on the hands of Siva, when he married the mountain goddess Parvati.
The system formed by the rivers Karatoya, Atrai, Gur, Gumani and Hurasagar has a total length of about 597 km and is free from tidal influence. [Masud Hasan Chowdhury]
See map in brahmaputra-jamuna river system.