The River Trent is one of the major rivers of England and its source is north of Stoke-on-Trent in Staffordshire. It flows south-east through the Northern Midlands and becomes navigable at Shardlow. The river then flows northwards through Nottingham with boats using the Beeston Cut and Nottingham Canal to by-pass the nearby shallows. It continues on through Newark to Cromwell Lock where it becomes tidal and eventually joins the Yorkshire Ouse at Trent Falls to join the Humber Estuary. At certain times of the year, the lower tidal reaches of the Trent experience a moderately large tidal bore of up to five feet high (1.5m). It is known as the Trent Aegir and occurs when an incoming high spring tide coming up the Humber Estuary meets the downstream flow of the river. The northern limit for narrowboat navigation is normally Keadby, just north of Gainsbrough where the Stainforth & Keadby canal joins the River Trent. Sea-going vessels can be found on the tidal section north of Keadby.