Stunning two-tone sea phenomenon appears in Cardigan Bay in west Wales, UK

A stunning two-tone sea colour phenomenon appeared off the coast of Aberystwyth in west Wales in the UK on Sunday (May 16). The sea appeared to be perfectly divided into two very different shades of blue at the harbour entrance where the River Ystwyth and Rheidol flow into Cardigan Bay. The phenomenon happens when colder freshwater with organic matter in it meets the warmer salty ocean in such a way that they do not immediately mix. This only happens when the sea is calm and the rivers are high after heavy rain. "You can see the clear blue sea divided at the exact point where the rivers flow in," said the filmer Scott Waby.