The Merioneth area remains one of the strongest Welsh-speaking parts of Wales, although places like Barmouth and Tywyn are very Anglicised. The coastline consists alternately of cliffs and stretches of sand and the area generally is the most mountainous in Wales; a large part of the Snowdonia National Park lies within it. The highest point (county top) is Aran Fawddwy near the village of Dinas Mawddwy at 905 m (2,970 ft), which is also the southernmost mountain in Great Britain to exceed an altitude of 900 metres. However, the mountain of Cadair Idris 893 m (2,929 ft) to the south of Dolgellau is better known and hugely popular with hillwalkers. Other mountains include Arenig Fawr and the Rhinogydd. The chief rivers are the Dwyryd, the Mawddach, the Dyfi and the Dee, while in the south the Dulas forms the county boundary. Waterfalls such as Pistyll Cain and small lakes are numerous, the largest being Bala Lake (4 miles long and broad).