Hilfield Park Reservoir

From Londonbirders

Hilfield Park Reservoir (map; OS grid reference TQ157959) is a local nature reserve in Hertfordshire, sandwiched between Elstree Aerodrome and the A41 and M1 routes into (and out of) London.

The reservoir has a storage capacity of about 600 million gallons (2,700 megalitres), which is enough to make 11 billion cups of tea. It covers an area of about 115 acres (46 hectares — or 65 football pitches, if you prefer) and is surrounded by 80 acres (32 hectares) of woodland, grassland and scrub.

Because access is restricted, the reservoir is notable among London-area sites for its lack of disturbance. Birders denied access can obtain distant views from two awkward viewpoints. The site’s most interesting bird is a species that is mentioned below but is mysteriously (?) absent from the trust’s annual review.



Hilfield Park Reservoir was constructed in the early 1950s as a reservoir for drinking water, although it is not currently used for that purpose. It was established as a local nature reserve in 1969 in an agreement between Three Valleys Water Services Plc (now Veolia Water Three Valleys) and Hertfordshire County Council. Management is undertaken by the Hertfordshire and Middlesex Wildlife Trust.


Fed by water from the chalk aquifer, the reservoir supports abundant aquatic weeds, including stoneworts. A lack of islands is compensated for, to an extent, by a couple of rafts, on which a few Common Tern nest, and a floating Sand Martin bank installed in 2008. Around the margins of the reservoir are large boggy areas where many species of marsh plants flourish, including reed mace, reed canary grass and various sedges. The reservoir is surrounded by woodland, rough grassland and invading oak and bramble scrub, which is all managed to encourage a diversity of species.



In winter, the reservoir is a refuge for large numbers of ducks, particularly Mallard, Shoveler, Teal, Wigeon, Pochard, Tufted Duck and Goldeneye. Scaup, Common Scoter, Goosander and Red-breasted Merganser are also possible. Especially after easterly winds or in harsh conditions, the site can also harbour Divers and Red-necked, Slavonian and Black-necked Grebe. The site has a gull roost that can contain Mediterranean Gulls.

In spring, passage migrants include Black-necked Grebe — sometimes well into double figures — and the occasional Red-necked or Slavonian Grebe. Ducks may include the odd Garganey, Common Scoter, Scaup and Red-breasted Merganser. Passage raptors include the occasional Osprey. Wader species pass through in small numbers and include Oystercatcher, Grey Plover, Little Stint, Dunlin, Whimbrel and Turnstone. Little Gull, Sandwich Tern, Arctic Tern, Little Tern and Black Tern are all seen on occasions. Passerines seen on the embankment include Larks, Pipits, Wagtails, Wheatear, Whinchat and the occasional Redstart.

In summer the site supports breeding Sedge Warbler, Reed Warbler, Whitethroat, Garden Warbler, Blackcap, Chiffchaff and Willow Warbler, along with Common Tern (about 10 pairs), various common waterbirds and Hobby. Buzzard have also bred in recent years.

A species list for recent years is available at the British Trust for Ornithology BirdTrack website.


More than 20 species of butterfly and more than 15 species of dragonfly and damselfly have been recorded at the site. The Ruddy Darter Dragonfly returned in 2008 after an absence of six years.



From London, the site is most easily approached along the A41 Watford road. About 1km north-west of the A411 (Bushey–Elstree) roundabout, keyholders should turn into Hilfield Lane and after about 300m turn right into the water company car park, locking the gate behind them. Those less privileged can attempt to park on the verge in Hilfield Lane or turn back along the A41 to park in a lay-by and then cross the A41 to a footbridge over the M1 (map; OS grid reference TQ154955), which offers a rather distant view of the reservoir. Alternatively, south-east of Hilfield Lane, turn off the A41 into Dagger Lane and then left into Hogg Lane. Park just inside the Elstree Aerodrome site and take the public footpath south across a field (typically very muddy thanks to the hooves of its resident horses) to reach a viewing platform (map; OS grid reference TQ159961) offering an equally distant view across the water.


There is no public access to the site. Access is restricted to members of the Hertfordshire and Middlesex Wildlife Trust, although escorted visits are occasionally possible through local wildlife groups. Once inside the site, visitors must negotiate a long flight of steps up the reservoir wall. Good walking shoes or wellies are recommended. Those denied access must either risk their lives walking the high-speed, pavement-less A41 in an attempt to reach the M1 footbridge or risk losing their boots in the boggy approach to the viewing platform near the aerodrome.


Apart from a single hide on the south shore of the reservoir, there are no facilities on site for those lucky enough to gain access.

Refreshments are available locally at the 3 Greens Restaurant at Elstree Aerodrome (open daily from 9am) (map). Somewhat more basic refreshments (along with a limited range of Winnie-the-Pooh characters) can be obtained from the Aldenham Country Park refreshment kiosk, which can be reached on foot from Dagger Lane or by car (if you can afford the £5 parking fee) from Aldenham Road (map). The kiosk is open daily from Easter to the end of October and at weekends throughout the year, weather permitting.

Two local hostelries serve good pub food. For birders, the better choice is the Fishery Inn, on the A411 Elstree Road/Watford Road map because its “outside eating terrace” and its large windows offer views of waterbirds on Aldenham Reservoir (which the pub’s website manages to describe as “Aldermaston Lake”). And the staff are friendly too. Less appealing ornithologically (and also culinarily, if that is a real word) is the Battle Axes (which doesn’t seem to have its own website), at the junction of Aldenham Road and Butterfly Lane (map).

This information has been cobbled together from various sources by Andrew Haynes, who has eaten at the Fishery Inn and the Battle Axes but has never actually had access to the reservoir, even though he was once briefly a member of the Herts & Middx Wildlife Trust.

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