can dissolve, leading to cracks and joints forming and enlarging. In areas where limestone is at the surface, with very little soil cover, water will drain underground through these cracks rather than running off overground through river and stream systems. The water can then flow underground, emerging later at springs. At times of higher rainfall, the water table will rise, as the underground flow cannot drain all the water, and turloughs will then fill. When the water table drops they will empty again. Turloughs will usually have specific place on the floor where water flows in and out, called a swallow-hole (slugaire in Irish). Sometimes an actual hole can be seen, but more often it is a hollow filled with stones. In some larger turloughs the hole will be permanently wet, allowing fully aquatic plants and animals to survive. Various attempts have been made to classify turloughs into distinct types, such as highland and lowland, fast fluctuating and seasonally fluctuating, or more complex schemes. However, a recent study using multivariate analysis of a wide range of variables characterizing the water bodies shows that there are no distinct types, but rather a continuum from wet to dry. Flora Turloughs usually have a mixture of aquatic and terrestrial vegetation, occurring in zones depending on the water depth and frequency/duration of filling. In Ireland, the deepest part is characterised by aquatic and semi-aquatic plants such as Chara, Ranunculus, Potamogeton, Littorella uniflora, Polygonum amphibium and Mentha aquatica. This gradually gives way to a sward of Potentilla anserina, sedges such as Carex panicea, and Viola species. The black turlough moss Cinclidotus fontinaloides grows on surfaces such as rocks and tree trunks. Further up the sides of the turlough shrubs like Frangula alnus and Potentilla fruticosa occur. Some turloughs will instead transition to fen vegetation including sedges and bogbean (Menyanthes trifoliata). Another characteristic feature is the growth of layers of filamentous algae during warm and dry weather, which later dry out and form "algal paper". Fauna The intermittent nature of these temporary water bodies provides challenges to aquatic animal life. The organisms commonly found in them have adapted various survival strategies, such as aerial adult forms, production of desiccation-resistant resting stages, and amphibious lifestyles. Fish are usually absent (although in larger turloughs sticklebacks can survive by retreating into the swallow-holes), and frogs and newts may sometimes spawn in them. The lack of predatory fish allows some