This is a real oddity. A lake that works like a kitchen sink.
Loughareema lake in Antrim sits on a chalk ‘plug hole’ which sometimes gets jammed with peat, causing the depression to fill with water. When it clears, the lake drains underground at a rapid rate.
Just like a kitchen sink with a plughole at the bottom, the water fills up when the fill of the water is greater than the rate of how the water can leave. The lake empties in about 4 to 6 days during a good dry period. It can fill in a period of 12 to 18 hours.
The following video contains a time lapse movie of the lake transforming throughout the year: