Waveney and Little Ouse Valley Fens IPA

Location: Norfolk/ Suffolk Border between Diss and Thetford

Grid Reference: TM 047 799

The flat, wide headwaters of the Little Ouse and Waveney rivers are filled with fen – vast areas of reed and rush. This watery landscape is home to the largest surviving valley fen in England and special wetland plants like bladderworts, stoneworts and marsh orchids.

This Important Plant Area is home to:

  • An exceptional diversity of vascular plants and stonewort algae growing in lime-rich fens.
  • Some of the top 5% of lime-rich fens with great fen sedge in the UK.
  • Some of the top 5% of purple moor-grass meadows in the UK.

    These fascinating low-lying landscapes were formed 300,000 years ago, when glaciers carved out large river valleys as far south as East Anglia. Filled with chalk, clay, sand and gravel, they flooded when the glaciers retreated leaving a mosaic of large lakes along the valleys. Over time, these filled with thick layers of peat which, depending on the nature of the underlying deposits, are sometimes acidic and sometimes lime-rich. Only 43 of these fen mires survive the UK.

    We have also shaped the landscape here, with centuries of digging for peat and cutting reeds for thatching. More recently, drainage and water abstraction nearly brought an end to the fens, but many have now been saved. As water levels have returned, so has the wildlife which is thriving once more.

    Well over 270 species of plants are known from the fens. Pools of open water can be clothed with floating frogbit and duckweeds and often support rich growths of stonewort. These are large freshwater algae – rather like pond seaweeds – and nine species are known here, including lesser bearded stonewort, hedgehog stonewort, delicate stonewort and dwarf stonewort. Remarkable insectivorous plants called bladderworts are also to be found. These float in the water and their branching roots carry bladder-like traps that ensnare water fleas and other insects.

    On the edges of the water large stands of reeds develop, interspersed with sedges and rushes such as great fen sedge. With their feet in the water, these are joined by great willowherb, spearwort, meadowsweet, marsh marigold and nettle. This is also the home of the great raft spider, Britain’s largest spider with a body an inch long and which survives in just four sites in the UK.

    Away from the standing water, the fens are slightly drier and support many marshland flowers. The beautiful grass-of-Parnassus flowers here in summer, along with rare cowbane and narrow-leaved marsh orchid. Marsh lousewort provides splashes of purple and in less acidic spots insectivorous butterbur and sundews thrive.

    Where the fen has dried out a little, swampy woodland, known as ‘carr’ has developed. These thickets are formed from aspen, alder and birch and provide valuable habitat for birds and invertebrates. Fewer different plant species grow here than in fen, but where the light can still penetrate, plants such as marsh marigold thrive in pockets of wet soil.

    In slightly drier areas where chalky deposits come to the surface, fen-meadow has developed where the grass is cut for hay and grazed by livestock. Dominated by purple moor-grass, many special plants grow here including meadow thistle, ragged Robin and black bog-rush, all accompanied by a wonderful array of orchids such as marsh fragrant orchid, early marsh orchid and southern marsh orchid.