Redgrave and Lopham Fen is the largest remaining example of the ancient valley fen system of North Suffolk which lay along the valleys of the Little Ouse and Waveney.

Valley fens have suffered a dramatic decline throughout Europe because of drainage and people's use of water. In the UK there are only 43 valley fens left. Of all eco-systems in the UK, fens are one of the most valuable botanical resources, with a large range of plant species, including many that are uncommon and declining and several that are already rare.

It's the chalky water that makes a fen...

Fens are like bogs, swamps and marshes, in that they are areas of waterlogged land supporting a wide variety of plants and animals adapted to live in damp conditions. Bogs, swamps and marshes are fed by rainwater, or water draining from the land (known as "run-off"), which makes them acid. Fens on the other hand, though often formed, like bogs, on waterlogged peat, are usually fed by water from below ground, which tends to be alkaline (chalky). For this reason, fens have a unique variety of plants and animals, all depending in some way on alkaline ground conditions.

...and it comes from the rocks below

A valley fen, such as Redgrave and Lopham, can be thought of as a peaty sponge, soaked with chalky water. These valley fens are unlike the fens of the 'great level' to the west, or the fens round the margins of the lakes and rivers in the Broads to the northeast. Those are fed by rivers draining the higher ground of central East Anglia. The valley fens, however, depend on the water welling up from deep below and on water from springs at the head of the valley. These springs arise where the layer of glacial sand, meets the underlying boulder clay. Water seeps down through the sand, and then unable to go on down through the clay - finds its way out in the form of a spring or line of springs (known as a seepage line).

It is generally believed that a continuous strip of valley fens extended from the head of the valley, along the valley floors, merging with the floodplain fens in the lower stretches.

It began with the ice...

The origin of the valley fens goes back 300,000 years to the last ice age. It was at this time that the glaciers carved what are today the Ouse and Waveney Valleys. These glaciers pushed towards Britain from Scandinavia and carried with them chalk, clay, sand and gravel, all of which were deposited within the Waveney and Ouse valleys, both along the valley edges and in patches within the valley basin.

As the glaciers melted, the valleys flooded. Then as water levels fell, a series of large lakes were formed along the valley lines. The aquatic plants quickly moved into these still bodies of water, as environmental conditions improved. When these plants died and the lakes slowly silted up other species colonised the lakes the whole process of change from lake to fen began.

...and was followed by peat

The fen vegetation became established across the old lake surface - and whenever fen vegetation becomes established, fen peat is formed. The waterlogged nature of this ground ensures that there is little oxygen available for the decomposed micro-organisms to bring about the decay of plant material. This litter gradually builds up as successive generations of fen plants grow and die. It later develops into a thick mat which is slowly compressed to become peat. This is a fibrous soil, which is entirely organic. It is generally believed that the constant flow of chalky water from the springs and seepage lines would have been impeded by the growth of fen vegetation. This would have brought about the rise in the water level of the lake basin, which in turn initiated the upward growth of the fen peat.

The initial plant colonisers of the lakes were entirely aquatic, but as peat accumulated, the lakes became shallower. Eventually plants were able to root on the lakebed whilst having leaves which emerged from the water. Further build up of peat saw the lakes completely filled in and colonised by terrestrial plants, which could withstand wet conditions. Normally the next stage in the succession of these lakes would be the establishment of woodlands and a general drying of the surface. However, in these isolated valleys both man's activities and the presence of underground springs have halted this.