A lake-burst (Old Irish: tomaidm[1]) is a phenomenon referred to in Irish mythology, in which a previously non-existent lake comes into being, often when a grave is being dug. Part of the lake-burst stories may originate in sudden hydrographic changes around limestone-based inland plains or turloughs. […]

Medieval bards had a special genre of lake-burst poems called tomamond.

Source: Lake-burst – Wikipedia