At just under 6 miles (9.7 km) long, it is one of the shortest classified main rivers in the country.

From the confluence it flows south-east of the village of Tholthorpe, near Easingwold, past Flawith, Alne and Tollerton.

At Linton-on-Ouse it turns south and joins the River Ouse just north of Newton-on-Ouse.

The name of the river derives from the Brittonic *cǖl, meaning "narrow" (Welsh, Cornish and Breton cul).

[8] There are two Ordnance Survey Leisure Walking routes that cross the river near Tollerton.