Welsh coast are the OBel Sands, an extensive area of sand waves up to 62' (19 metres) high, covering an area of over 400 sq. mi. (1,000 km2). Ecology The Bristol Channel is an important area for wildlife, in particular waders, and has protected areas, including national nature reserves such as Bridgwater Bay at the mouth of the River Parrett. At low tide large parts of the channel become mud flats due to the tidal range of , frequently stated to be second only to the Bay of Fundy in Eastern Canada but smaller than those at Ungava Bay, also in Canada. Development schemes have been proposed along the channel, including an airport and a tidal barrier for electricity generation, but conservation issues have so far managed to block such schemes. The largest islands in the Bristol Channel are Lundy, Steep Holm and Flat Holm, which are mostly uninhabited and protected as nature reserves, and are home to some unique wild flower species. In 1971 a proposal was made by the Lundy Field Society to establish a marine reserve. Provision for the establishment of statutory Marine Nature Reserves was included in the Wildlife and Countryside Act 1981, and on 21 November 1986 the Secretary of State for the Environment announced the designation of a statutory reserve at Lundy. There is an outstanding variety of marine habitats and wildlife, and a large number of rare and unusual species in the waters around Lundy, including some species of seaweed, branching sponges, sea fans and cup corals. The Bristol Channel has some extensive and popular beaches and spectacular scenery, particularly on the coasts of Exmoor and Bideford Bay in North Devon and the Vale of Glamorgan and Gower Peninsula on the Glamorgan coast. The western stretch of Exmoor boasts Hangman cliffs, the highest cliffs in mainland Britain, culminating near Combe Martin in the "Great Hangman", a 1,043 ft (318 m) 'hog-backed' hill with a cliff-face of 820 ft (250 m); its sister cliff the "Little Hangman" has a cliff-face of 716 ft (218 m). On the Gower Peninsula, at its western extremity is the Worms Head, a headland of Carboniferous Limestone which is approachable on foot at low tide only. The beaches of Gower (at Rhossili, for example) and North Devon, such as Croyde and Woolacombe, win awards for their water quality and setting, as well as being renowned for surfing. In 2004,