The site lies in the Mimram valley, and contains a variety of habitats including
wet meadow, tall fen / swamp, alder carr, willow scrub, willow pollards and chalk
stream.
The tall fen/ swamp occurs around a lagoon (overlooked by a hide) and along adjacent
channels, and has a mixture of common reed, reed sweet-grass and common reed-mace.
Willow scrub has been slowly invading the lagoon, but has been kept under control by
Trusts staff and volunteers. During 2006 and 2007 considerable work has been undertaken
to make the swamp much wetter by removing silt build up and raising water levels.
This work, combined with the removal or pollarding of willows, encourages recolonisation
by common reed.
Wetland plants associated with the swamp include hemp agrimony, common comfrey,
reed canary grass, water figwort, brooklime, water forget-me-not, marsh marigold,
hairy willowherb, lesser celandine, yellow flag, purple loostrife, ragged robin
and wild angelica. The surrounding banks support great horsetail, butterbur and
town hall clock. There remain remnant tussocks of greater tussock sedge, a species
now uncommon in Herts.
The swamp area is important for both wintering and breeding birds. In winter, reed
buntings, yellowhammer and pied wagtail form night-time roosts in the swamp and carr.
Breeding species include reed bunting, reed warbler, sedge warbler and occasionally
grasshopper warbler. Mallard, coot, and moorhen also breed. Other species of note
include kingfisher, water rail, snipe and woodcock. The site is also a passage stop-over
for migrating warblers and other wetland birds.
The wet meadows vary in composition with the soils. Species here include meadowsweet,
cuckooflower, greater birds-foot-trefoil, marsh horsetail, marsh thistle, skullcap
and monkey flower. Marsh pennywort and southern marsh orchid, both uncommon in Herts,
can be found. The alder carr woodlands around the meadows have notable species
opposite-leaved golden saxifrage and remote sedge. Flocks of siskins and redpolls
feed in the woodland during winter.
The River Mimram is a valuable chalk stream with a rich aquatic flora and fauna.
River water-crowfoot, water starworts, water cress and lesser and greater pond sedge.
Many different aquatic invertebrates have been recorded. Brown trout, water vole
and otter can all be found within the stream.
Other species recorded include 3 shrew species, harvest mice and 5 species of bat.
Parking can be found on the road down to the Tewinbury Hotel; please park considerately
to other road users. A hide is adjacent to the road for use by visitors;
the key can be collected from hotel reception.