The Severn Estuary (Mor Hafren in Welsh) is fed by the rivers Severn and Avon and flows into a stretch of water known as the Bristol Channel forming a natural border between England and Wales. The estuary has historically formed an obstacle to people travelling from southern England to South Wales. In Victorian times it was necessary to break one's journey from London and to cross the river by ferry before rejoining the train. The river is renowned for its treacherous tides, especially during bad weather, so in 1873 work began on building a tunnel. The tunnel was completed in 1886, but not before overcoming the major obstacle of blocking off the Great Spring, a natural fresh water spring, which flooded the tunnel on numerous occasions. (To this day 50 million litres/day of water has to be pumped out and is sold to the local Water Company.) Numerous bridges have also been built across the water, the latest being The Second Severn Crossing, completed in 1996, which carries the M4 motorway between England and Wales and is a masterpiece of engineering.

The Severn Estuary has the second highest tidal range in the world at 8.8m (the greatest being at the Bay of Fundy in Canada at 10.8m). An unusual feature is the Severn Bore - a strange phenomenon where the rising tide hits the outflow of the river, resulting in a wall-like wave which progresses upstream for as much as 50 miles. The brackish waters of the estuary are laden with fertile silt and the waves look like liquid mud as they roll onto the riverbanks and shores. The resultant mud banks are a haven for wildlife and provide overwintering for many species of wild birds; in 1946 Sir Peter Scott opened the Wildlife and Wetland Centre at Slimbridge, where the visitor can enjoy seeing the largest collection of geese, ducks and swans in the world. The estuary is of great ecological significance and is a designated Special Protection Area, with many Sites of Special Scientific Interest (SSCI).

The estuary is also an important fishing region and is particularly famous for its elvers (or glass eels). Between March and April each year these young eels make their long journey up the Severn, having hatched three years earlier in the Sargasso Sea on the other side of the Atlantic Ocean, only to be caught in huge quantities by elver fishermen. Once available in abundance these tiny eels have now become scarce - what was once traditional country fare is now deemed to be a great gastronomic delicacy (something to do with their supposedly having aphrodisiac properties?) and fetches enormous prices resulting in over-fishing. Other fish to be found in the estuary include cod and salmon, stocks of which are also critically low. A ten-year ban on salmon fishing could be imminent and the old ways of catching salmon using wicker baskets may be lost in this time.

The huge tidal range of the Severn Estuary put it at risk of being developed for both tidal and wave power generation schemes. The Severn Barrage Committee was set up just after the oil crisis in 1978 to research the feasibility of such a project. While sources of renewable energy are welcome, the strain on the ecology of the region could be catastrophic and no one can accurately predict what effect the building of barrages etc. would have in this environmentally sensitive region.

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