Unlike most reservoirs and lakes in the London area, Brent Reservoir has natural margins and is surrounded by a diverse habitat that includes swamp, fen, willow carr, rough grassland, woodland, hedgerows, allotments, playing fields and suburban gardens.
The reservoir covers an area of some 170 hectares (420 acres, 0.66 sq mile). It has deep areas that attract diving waterbirds as well as mud-fringed shallow margins that suit dabbling ducks and waders.
Unusually for a wetland site, the reservoir is distinguished by the debris that fetches up at its marshy east end (where the WHCG has its hides). This rubbish has either been washed down the River Brent or blown along the reservoir by the prevailing wind. Wildlife does not seem to be deterred by the garbage, which includes dustbins and wheelie bins, road cones and traffic bollards, car seats and bumpers, supermarket trolleys, garden chairs, plastic buckets, footballs, bottles and cans. Brent Reservoir has an advantage over most other wetland birding sites in that this detritus can provide useful markers for anyone trying to point out a distant bird (e.g., “There’s a Little Stint out there, feeding just in front of a Coke can between the yellow plastic bucket and the traffic bollard”).
The site includes substantial areas of rough grassland. One, known to local birders as “the Shrike Field” (because a Great Grey Shrike spent a few days there in autumn 2008), abuts the north bank of the main reservoir. Another, known as “the Dump” (because it was a rubbish dump until turfed over in 1970), is above the reservoir’s northern arm.
The site has several woodland areas. North of the dam is a stand of mixed woodland, and a small oak wood straddles the Brent/Barnet boundary next to the reservoir’s north bank. Mature willow woodland can be found at the eastern and northern extremities of the reservoir.
The site includes a significant length of ancient hedgerow, which attracts breeding passerines, including Lesser Whitethroat.
Part of the site was developed as allotment gardens after the second world war. Some of the plots are now disused and have become overgrown, presenting a tangle of shrubbery that attracts a range of passerine species, particularly warblers.
Playing fields cover a significant part of the area, providing feeding opportunities for thrushes, crows, gulls, etc, and also attracting passage migrants such as Wheatear.
The gardens of houses backing on to the site provide secluded lawns and other feeding areas for many bird species. Bird feeders in some of these garden also help the survival of wintering passerines.