Home to rare and threatened species

With a high peat content and water table, fens support many threatened plant and invertebrate species. These internationally important wetlands have declined massively due to changes in land use, lack of management and pollution. 

What is a fen?

A fen is a wetland that is largely sourced from groundwater, including springs and seepages etc, or surface water, such as rivers or rainwater runoff.

Fens are usually peat-forming habitats and the water table is near the ground surface for much of the year.

The term ‘fen ‘encompasses many different types of wetland, from poor-fens, such as valley mires, to rich-fens, including alkaline fen. Although bogs share many of the same plants and animals as fens, they are predominantly rainwater-fed.  

Aerial view of fen with trees around it.

- Coleshill fen at the National Trust Coleshill estate.

10 km2

of fen habitat in England today


plant and animal species live in fens


of all UK native plant species are supported by fens

10 km2

of fen habitat in England today


plant and animal species live in fens


of all UK native plant species are supported by fens

What can we find living in fens?

With a high peat content and water table, fens are highly diverse habitats, supporting many endangered plant and animal species.

Some examples of rare fen plant species are Slender Green Feather Moss (Hamatocaulis vernicosus), Crested Buckler-fern (Dryopteris cristata) and Fen Orchid (Liparis loeselii). Fens are home to a very special invertebrate community, with astonishing diversity in groups like, beetles, dragonflies, molluscs, moths and soldierflies. Among the vertebrate visitors of fens, we can find Water Vole, Bittern and several species of newts.

Species directory
Orange coloured moth on a pink flower with raggedy petals.

- Large Skipper (Ochlodes sylvanus) on Ragged Robin at the alkaline fen at Lye Valley, Oxford. Photo: Dr Tony Gillie

Why are fens important? 

Fens support a wide array of wetland species – some of them very rare and not found anywhere else. So, they are extremely important for UK’s biodiversity.

In addition, fens usually form peat, a layer of organic material formed by the partial decomposition of plant material that is a vital carbon sink. This also helps with flood control and providing habitat for wetland wildlife.  

Our policy work
Aeriel view of field with electricity pylon ad people working.

- Hinksey Heights, Oxfordshire. Photo: Tim Bearder.

What threats do fens face?

It is estimated that 3,400 km2 of fen was present in England in the 17th century, but only 10 km2 remains today. 

The cause of this decline is complex and the result of a number of factors. Lack of management and livestock grazing has led to many fens being encroached by trees and scrub. The use of fertilisers in nearby arable land is also impacting on fens, which have impermeable surfaces, preventing infiltration. Many historic fens have been drained to use the land for commercial purposes, including farming.

Climate change brings additional threats, with less reliable rainfall and increasing summer droughts that could affect the water table and threaten the survival of our remaining fens. 


Fen violet

- Fen Violet.

How Freshwater Habitats Trust is helping fens

Freshwater Habitats Trust is restoring fens by managing and rewetting them. This is halting biodiversity loss and carbon emissions in these special habitats. We are also supporting landowners and managers with funding and advice, bringing best management practice to fens. To understand more about these habitats and the species they support, we monitor and study fen vegetation and hydrology .

We are raising awareness about the fen habitat through environmental education and community engagement. We have developed the rare plant community project GroWet, which involves local people in reintroducing plants to fens in Oxfordshire, and use social media and events to reach the public. 

With our partners and a committed team of volunteers, we run the Oxfordshire Fens Project to reverse fen decline in the county. 

The Oxfordshire Fens Project
Aerial view of fen with trees to the right and a path to the left. People working on the land with tools.

- Volunteers restoring Coleshill fen in partnership with the National Trust.

Find out more about our work on fens

Aerial view of alkaline fen with people raking and scything and electricity pylon.
The Oxfordshire Fens Project

With partners and volunteers, we’re protecting the county’s internationally important alkaline fen habitat for the future

Find out more
Three women holding plants in pots, standing outside a greenhouse

Through our GroWet project, people across Oxfordshire are helping us nurture rare and threatened plants.

Find out more
Aerial view of a landscape, including a meandering river and newly dug ponds.
The Freshwater Network

Together, we’re building a national network of wilder, wetter, cleaner, more connected habitats to reverse the decline in freshwater biodiversity.

Find out more