The River Trent is one of only two rivers in England to have a tidal wave (the other being the River Severn). Named after Aegir, the chief of the Sea Giants in Scandinavian mythology, the best time to see the Trent Aegir is in the Spring, and the banks of the river in Gainsborough provide an excellent viewing place.

Like the Scandinavian sailors in the myths, river people treat the coming of the aegir with great caution as it is very unpredictable and capable of damaging boats. In the days of small craft it was the custom to shout 'Ware Aegir' to warn of its approach.

 

This photo was taken by a friend of mine, and clearly shows the approaching wave.
Click on the image for a larger photo (will open in a separate window).