Sewardstone Marsh (Map:; OS grid reference TQ378982) is a site of about 14.5 hectares (36.5 acres) within the Lee Valley Park. Its two main areas, Knights Pits and Patty Pool Mead, provide marshland, two small lakes and a seasonally wet area.
Address: Sewardstone Marsh, Godwin Close, Sewardstone Road, London E4 7RQ
The marshes were originally grazing meadows but with the discovery of gravel for use in road building, the area was excavated during the 1939–45 war. The land was then sold to the North Metropolitan Power Station, which used the area as a dumping ground for pulverised fly ash and rubble from the nearby Brimsdown power station.
Lee Valley Regional Park Authority has owned Sewardstone Marshes since the mid-1980s, It was then surrounded by open fields and nurseries, with the Royal Ordnance Factory to the north and the Royal Small Arms Factory to the west. The site was designated a Site of Specific Special Interest because its disturbed ground and poor soils encouraged Early Marsh Orchids. Unfortunately, this delicate plant has disappeared as woodland has spread and shaded its growing sites.
The Knights Pits area consists of two pits formed as a result of gravel extraction, a large wooded area and some grassland and scrub. Patty Pool Mead, to the south of the site is a grazed meadow that regularly floods in winter and early spring. Work is taking place to improve the wetland to attract more birds. The site also includes a woodland copse and an extensive area of couch-dominated grasslands with invasive Elder and Willow scrub. There is also a track heading south between Patty Pool Mead and the River Lea. Patty Pool Mead is close to the KGV reservoir and species seen on the reservoir banks often flyover or feed on the site.
Hirundines amass in huge numbers during peak spring and autumn passage and a colony of Sand Martin breeds in the river wall drainage holes. Redwing and Fieldfare are regular, with big autumn passage counts possible. In winter, thousands of gulls fly in to roost on the reservoir and there is a huge Jackdaw roost in nearby Osier Wood.
The woodland surrounding the gravel pits is good for breeding and passage warblers including Garden Warbler. In autumn and winter, Goldcrest, Treecreeper, Siskin and Lesser Redpoll are regular, with Firecrest an uncommon visitor.
Northern Wheatear, Yellow Wagtail and Whinchat are annual on passage, with Common Redstart and Ring Ouzel also possible. These species, together with passage Skylark and Meadow Pipit, and Reed Bunting and Linnet, favour the east bank of the reservoir, and the bushes on Patty Pool Mead and perimeter fence-posts. In addition to passage Stonechat, a pair or two of this species sometimes winter.
Spotted Flycatcher is regular in autumn but scarce in spring, and Cuckoo is annual but declining.
Flyover passage terns and waders are a major feature, and the wet areas of Patty Pool Mead sometimes attract waders down to feed: Ruff, Grey Plover, Curlew, Black-tailed Godwit, and Little-ringed Plover have been seen here, and Redshank and Green Sandpiper are regular. Wintering Common Snipe are annual, with occasional Jack Snipe. At dusk, wintering Woodcock can sometimes be seen and heard flying south from the woodland and scrub to feed on the meadow.
Just off-site, the River Lea relief channel hosts a good variety of winter and passage duck including occasional Pintail, and, infrequently, Garganey. Goosander and Water Rail are regular in winter and Kingfisher is present all year along with Little Egret and Cetti's Warbler. Passage Common Sandpiper are sometimes seen on the concrete sills and small weirs.
Common Buzzard, Kestrel, and Sparrowhawk are regular, as is Hobby in summer and autumn, with occasional spring records. Red Kite and Peregrine sightings have increased, with the latter species sometimes observed on Brimsdown Power Station to the west of the site. Barn Owl is slowly increasing and Short-eared Owl is occasional on passage and in winter. Little Owl occurs but has declined.
Scarcities in recent years have included Long-eared Owl, Goshawk, Merlin, Osprey, Marsh Harrier, Raven, Pink-footed Goose, Twite, Lapland Bunting, Bearded Tit, Yellow-browed Warbler, Grasshopper Warbler and Water Pipit.
Around 90 species are recorded annually.
The larger of the two flooded pits is a fishery, with Mirror Carp, Pike and Bream.
On the site as a whole, most of the typical Lee Valley butterfly species have been recorded. The Musk Beetle, which depends on young Willow woodland for its breeding and development, can also be found.
Visitors approaching by car should head for Sewardstone Road (A112) and park in Godwin Close. The entrance to the site is at the end of the close. Bus route 505 passes the end of Godwin Close. Pedestrians may also approach the site from Swan and Pike Pool, walking along the River Lee and across an Environment Agency bridge into the marshes. From the north, the site can be reached through Gunpowder Park or across Cattlegate Bridge from Enfield Island estate. Cyclists can reach the site by following Section 18 of the Sustrans London Loop, which passes through the marsh. The nearest railway station is Enfield Lock, which is about 30 minutes walk to the west.
Tar and chip paths allow an easy circular route around the marshes and onto Epping Forest.
Along the pathways can be found a number of benches and picnic tables to encourage visitors to relax and enjoy their surroundings. Interpretation boards are currently being developed for the site.
I updated the Birds section above on 20 March 2019 - I am a regular visitor to the site (Martin Shepherd). Thanks to the person who put together the initial entry. If you are familiar with the site, please correct, expand and/or update this information.