Marlacoo Lake is labelled 15 on the map.

The lake was described in 1838 in the Ordnance Survey Memoirs: "Marlacoo lake, situated in the north eastern part of the parish 3 and a half miles south east of the town of Richhill, is situated 230 feet above the sea. Length from north east to south west 600 yards. Breadth from north west to south east 230 yards: It is partly in the townland of Marlacoomore and partly in Marlacoobeg [in the parish of Mullaghbrack]. "