The Severn Estuary is the largest, muddiest and most dynamic estuary in Britain, and thousands of birds use it every year as a stopping-off point on their migrations to and from Africa. Other migrants, including butterflies and fish, make use of it, too.

In fact, as Chris Sperring discovers, the Severn Estuary is a vital nursery ground for some of our most commonly-eaten marine fish; tiny sea bass make it as far as Gloucester before heading off back to sea. Show less