There are two known types of aquifer fed naturally fluctuating habitat in the UK:

1. Turloughs: These are flat-bottomed sinkholes found over limestone in Northern Ireland and Wales which are distinguished by winter flooding and dry conditions in the summer (although there may be some small residual pools). There may also be underground connections between neighboring turloughs which will affect their water level.
2. Fluctuating Mere's: These occur over chalk in the Norfolk Breckland and do not appear to have an annual emptying/refilling rhythm. Instead, sites may remain dry for several years before re-filling for longer periods, with smaller fluctuations causing changes in water level above ground at wet times.

This type of habitat is rare both nationally and internationally and the nutrient content of each site varies depending upon the groundwater quality. The water is always hard at this type of habitat as the underlying rock is calcareous.  

Vegetation zonation in these water bodies when dry is partly or completely grassland. Because of the temporary nature of this habitat, aquatic plants are not seen, but aquatic and semi-aquatic mosses such as the common water moss Fontinalis antipyretica and Cinclidotus fontinaloides (which are more resistant to desiccation), may be found. Woodland and scrub such as willow, birch, alder, ash and hazel, may also surround the area. The aquatic fauna that does inhabit these areas is adapted to desiccation.

Fish are usually absent from pools, but amphibians such as the great crested newt Triturus cristatus can be found. Mobile invertebrates such as water boatmen, diving beetles and dragonflies can colonise these water bodies and micro-crustaceans such as water fleas, which have dormant stages which tolerate dry phases, can also be found. During wet phases, fluctuating water bodies can support breeding coot, tufted duck, mallard, shelduck, pochard and gadwell.

The largest threat to this habitat is undoubtedly climate change. A marked change in rainfall patterns which supply these natural aquifers may lead to them becoming permanently dry, as the water table may not be high enough to reach the surface. Water extraction for human consumption or irrigation is therefore also a very large threat. As with all freshwater habitats, nutrient enrichment through the use of fertilisers, sewage effluent or livestock rearing is always a danger, as eutrophication could upset the biology of pools. Whilst stock grazing has its risks to fluctuating water bodies (such as nutrient enrichment and damage to the pools), an appropriate level of grazing is needed to dissuade the invasion of scrub vegetation. Conifer plantations close to water bodies may also pose a threat, as they negatively affect the water table.

The Breckland Mere's are designated as a Site of Special Scientific Interest (SSSI) and are also a proposed Special Area of Conservation (SAC) under the EC Habitats Directive. This area has also been designated as an Environmentally Sensitive Area (ESA) under the EC Common Agricultural Policy (CAP). The turloughs in Northern Ireland are designated as Areas of Special Scientific Interest (ASSI) and Pant-y-llyn, a Welsh site, is designated as a SSSI.

Research into this type of water body has been carried out by a number of different agencies. The Countryside Council for Wales (CCW) and the Environment Heritage Service (Northern Ireland) have carried out biological surveys on Pant-y-llyn in Wales and the turloughs in Northern Ireland. Ecological surveys of the Breckland mires have suggested a model to explain the fluctuations in water level.

In order to protect this type of habitat, actions with lead agencies have been proposed. These include:

• Ensuring that water abstraction and groundwater protection policies take into account the specific requirements of aquifer fed naturally fluctuating water bodies.
• Ensuring that fishery policy recognises the need to prevent introductions of fish to these water bodies.
• Continuing to review the use of water resources in the area affecting the hydrological balance of the Breckland Mere's
• Designating as SSSI/ASSI, all good examples of aquifer fed naturally fluctuating water bodies which are newly discovered and which lack such protection.
• Continuing to advise Government and landowners on measures to safeguard this fragile habitat.
• Contributing to knowledge of the status and importance of naturally fluctuating water bodies and of their effective management, by exchanging information gained in the UK with colleagues in other countries which contain similar sites.
• Developing and implementing appropriate surveillance and monitoring programmes to assess progress towards action plan targets.