Ynyslas National Nature Reserve is situated midway between Aberystwyth and Machynlleth. The 2,000-hectare National Nature Reserve covers three main areas: Dyfi estuary. The estuary includes vast areas of internationally important mudflats, sandbanks and salt marsh that provide important feeding and roosting areas for wetland birds. In winter, you will see a variety of birds of prey, such as hen harrier and peregrine falcon, and you might also catch sight of the Greenland white-fronted goose: this is its only locality throughout Wales and England. Ynyslas sand dunes. The superb dunes of Ynyslas are at the southern side of the estuary mouth and are the largest dunes in Ceredigion. They demonstrate all the stages of dune formation and growth, from sandy shore through the vegetated shingle, foredunes, mobile dunes and fixed dunes to scrub. They are home to a rich population of orchids, mosses, liverworts, fungi, insects and spiders; many of these species are rare and some are unknown elsewhere in Britain.