English: Tide waves (bores) like the Trent Aegir, one of the nation's most interesting and unusual natural phenomena, naturally occur on rivers with large tidal ranges. There are only two rivers in England that have a tidal wave. The 'bore' on the River Severn is well-known, the Trent's 'eagre' is less well-known, yet the tidal wave can travel as far as 50 miles upstream from Hull to Gainsborough. This natural phenomenon occurs in the lower reaches of a only a few rivers throughout the world during very high tides. This shot, taken just outside Gainsborough, this morning, shows the last Aegir of 2006 in a diminishing state have travelled almost 50 miles. – A bore is formed when the tide rises in a converging channel with a rising riverbed formed in a funnel shape. The name ‘bore’ as applied to the tidal phenomenon appears to be derived from the Scandinavian or Icelandic ‘bara’ meaning wave, swell or billow. The Trent Aegir, is named after the god of the seashore or ocean in Norse mythology and, like the Scandinavian sailors in the myths, river people would fear the aegir as it is very unpredictable and would sometimes surface to destroy ships. Sometimes the tide merely changes the flow of the river but, at its best, the wave breaks with fury as it passes by and causes damage to boats on the moorings or in its wake.