Fen and swamp habitats often occur together, forming complex mosaics in areas of waterlogged ground, the differences can be difficult to clearly define. Generally, swamps tend to be dominated by tall grasses, e.g. common reed (Phragmites australis), or scrub, while lowland fens can encompass a wide range of wetland types on wet acid, neutral or basic soils and with a more varied structure and composition. A naturally functioning wetland area would often comprise a mosaic of swamp, fen, transition mire and pool habitats. The key habitat components of swamps and fens are outlined briefly in the sections below.

Generally, the management of these habitats might involve light or moderate grazing by cattle and an avoidance of artificial drainage, peat-cutting, burning and afforestation.