HOUGHTON REGIS MARL LAKES is a Site of Special Scientific Interest (SSSI) notified under Section 28 of the Wildlife and Countryside Act 1981. The Lakes are an example of habitat type which is the rarest form of standing water in Britain confined to chalk or limestone areas with very few examples in southern England.
This extensive area supports a range of other species associated with wetland habitats including an outstanding assemblage of dragonfly, as well as being an important ornithological site in the county.
The two marl lakes are different in character, one is deep and steep sided while the other is a largeshallow lagoon. Characteristically for marl lakes they support an abundant Charophyte flora covering the lake bed. This includes both shallow water species such as Chara hispida (var. hispida) and deep water species such as Chara aspera. The clear waters support other aquatic species including curly waterweed Lagarosiphon major, horned pondweed Zannichellia palustris and spiked water-milfoil Myriophyllum spicatum.
The rich mollusc fauna associated with the lakes includes the species Potamopyrgus jenkinsi, a recent maritime colonist of freshwater typically found associated with beds of Chara in marl lakes.
Emergent vegetation has developed around the lake margins, particularly on the shallow lagoon including species such as common spike-rush Eleocharis palustris, common club-rush Schoenoplectus lacustris and various rush species Juncus spp.
Fen communities are associated with the waterlogged area between the lakes and where a feeder stream enters the shallow lagoon. Common reed Phragmites australis is locally dominant but elsewhere there is a mosaic of other characteristic species including water horsetail Equisetum fluviatile, marsh horsetail Equisetum palustre, lesser bulrush Typha angustifolia, lesser pond-sedge Carex acutiformis, hard rush Jancus inflexus and jointed rush Juncus articulatus.