Y Lefelau yw un o’r darnau mwyaf o gorsydd a ffosydd pori (reensfel y’u gelwir yma) sydd wedi goroesi ym Mhrydain a’r mwyaf o’u bath yng Nghymru ond mae’r cynefin hwn wedi bod o dan fygythiad oherwydd datblygu a llygredd.
The Levels are one of the largest surviving areas of ancient grazing marsh and reen(drainage ditch) systems in Britain and the largest of its kind in Wales but these features have been under threat from development and pollution.