In 1602 Sir Richard Carew saw fishermen catching oysters with 'a thick strong net fastened to three spills of iron, and drawn to the boat's stern, gathering whatsoever it meeteth lying in the bottom of the water, out of which... they cull the oyster'. When Les Angel and Timmy Heard show Alan Dein how they catch oysters in the Fal today he finds that, in four centuries, nothing's changed. The last wild native oyster beds lie in this beautiful Cornish estuary. In 1876, in an early example of conservation legislation, Truro Corporation passed byelaws forbidding the mechanised harvesting of oysters. The Fal oystermen use gaff-rigged cutters, some over a century old, the last in Europe to fish commercially under sail. Upstream they dredge with punts; not what see boys in blazers and girls in muslin poling along the Cam in, but hefty rowing boats. Twenty years ago mussel farming was introduced. Ropes are suspended from rafts, obliging molluscs attach themselves and grow, and grow. The methods are simple, the times, complicated. Carol Thorogood and David Robertson of Cornwall Port Health Authority take Alan up the Fal, explaining how they have to test shellfish. This summer some readings showed E coli present in concentrations above the limit; sections of the fishery were closed for a time, threatening fishermen's livelihoods. Out on the water Alan Dein meets Les Angel and Timmy Heard. The oysters have grown well; they're optimistic. But mussel-farmer Gary Rawle has abandoned the Fal, moving his rafts out to sea. The Fal has always flowed through farmland and towns. Is the water quality deteriorating, or being tested more rigorously? Alan ponders the future of the oystermen's precarious, wonderful way of life. Producer: Julian May.