Junction, where the Slough Arm branches off westward.

At suburban Cowley, before the 1930s a rural village, the canal begins to climb the valley of the River Colne north north-west into the adjoining town of Uxbridge. After Denham and Harefield villages, it passes to the south of Rickmansworth. Here it merges with the Rivers Chess, Colne and Gade. After Rickmansworth, the canal follows the valley