 The river contains over 80 islands.With its waters varying from freshwater to almost seawater, the Thames supports a variety of wildlife and has a number of adjoining Sites of Special Scientific Interest, with the largest being in the remaining parts of the North Kent Marshes and covering .The Thames, from Middle English "Temese", is derived from the Brittonic Celtic name for the river, "Tamesas" (from *"tamēssa"), recorded in Latin as "Tamesis" and yielding modern Welsh "Tafwys" "Thames".