In 1840 Cautley reported on the proposed Ganges canal, for the irrigation of the country between the rivers Ganges, Hindan and Yamuna (then called the Jumna), which was his most important work. Cautley began working towards his dream of building a Ganges canal, and spent six months walking and riding through the area taking each measurement himself. He was confident that a 500-kilometre canal was feasible. There were many obstacles and objections to his project, mostly financial, but Cautley persevered and eventually persuaded the British East India Company to back him. This project was sanctioned in 1841, but the work was not begun till 1843, and even then Cautley found himself hampered in its execution by the opposition of Lord Ellenborough.