A turlough is a karst lake, which has no surface outlet and is surrounded on all sides by rising land.

At Rahasane the drainage has been modified in that since the 19th century the Dunkellin River has followed an artificial channel downstream of the turlough, but part of the flow continues to go underground, via a natural sink, into the underlying limestone.

The site comprises marshes, and seasonally flooded wet meadows, with limestone outcrops and scrub at its margins.

The southern basin is the more impressive feature, with high rocky sides above an undulating base, strewn with boulders.

It is a very good place to spot accidental visitors from America, such as the American wigeon, and from Europe, such as the black tern.