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The Wash is a large rectangular-shaped tidal estuary in East Anglia bordering Lincolnshire and Norfolk.

Wildlife sound recordist Chris Watson has long been fascinated by both the mystery of King John's treasure - which it's claimed was lost and buried in the mud here - and the wildlife of The Wash.

A strange and haunting habitat, it’s a no man's land where twice each day the tide sweeps in across the mud and drives tens of thousands of wading birds off their feeding grounds and onto a temporary roost by the shingle and gravel pits at the RSPB reserve at Snettisham in Norfolk.

It's a bewitching spectacle, especially on a spring tide. At low tide the birds disperse and only the feint roar of the distant sea can be heard across the vast expanses of exposed mud. Beneath the mud however there are the sounds of crustaceans and worms; a rich food supply and the reason why so many thousands of birds are attracted to The Wash.

As the tide turns, rivulets of water trickle across the mud. The tide gathers pace, and as it does it so, it forces the birds towards the shore and into the air. Huge flocks numbering hundreds then thousands of birds are pushed off the mud and onto the gravel pits.

When Chris visited, the birds were roosting well away from the water and in complete darkness. Yet soon after the tide turned and by some unknown signal the knots' chattering calls increased and then the leading edge of the flock suddenly took off, creating a huge wave of sound.

Within a few minutes quiet and calm was restored to the gravel pits.

For Chris, it's these wild sounds of the birds revealed as the tides ebb and flow which are the real hidden treasures of The Wash.

Producer: Sarah Blunt

First broadcast on ´óÏó´«Ã½ Radio 4 in 2015.