Broadwater is a large gravel pit in the mid-Colne Valley. Included within the site are two smaller pits (Harefield and Korda Lakes), a section of the River Colne and adjacent woodland. It is a reserve managed by Herts. and Middx. Wildlife Trust.
This nationally significant wildfowl site is currently threatened by the Government's agreed plan for the HS2 (high speed rail) line. At this point there will be a high level viaduct across the lake. It may not be too late to change this - the HS2 tunnel under parts of Ruislip could, conceivably, be extended under the lake.
Access is off Moorhall Road running between Harefield and Denham Green. Unfortunately there is no car park, but it is possible to park on the road near Harefield, or on one of the small side roads at the start of Denham Green. Enter the site through a gate with a Herts and Middx Wildlife Trust sign just east of the River Colne. A footpath runs up the west bank of Broadwater, with two hides and several interpretive noticeboards. Another footpath runs along the causeway between Broadwater and Harefield Lake. This can get overgrown at times, but allows views over Harefield Lake.
The 331 bus runs along Moorhall Road.
Good numbers of wildfowl winter, with hundreds of Tufted Duck and Coot, good numbers of Pochard, Mallard, Shoveler, Wigeon, Gadwall and Goldeneye and a few (usually single figures) Teal present. A couple of Goosander often fish the river, while Korda lake often holds Smew (although Stockers is often a more reliable site for them).
Evening visits are often productive in winter, as there is a large gull roost with over 1000 Black-headed Gulls and several hundred large gulls. Great Black-backed Gulls and Yellow-legged Gulls are regular, while Caspian Gulls and Iceland Gulls have been found in recent years. Little Egrets roost on the islands viewed from the causeway, as do hundreds of Jackdaws. Several hundred Greylag and Canada Geese fly in for the night, often accompanied by Egyptian Geese.
In 2009/10 around 15 Chiffchaffs wintered on the River Colne, surviving on flies living in the weed mats on the river. Siberian Chiffchaff and Firecrest have been found along the river in recent years. Water Rail and Grey Wagtail also winter along the river, while the woods on the far bank hold a good range of woodland birds.
Passage waders tend to drop in to the gravel spit on Harefield Lake, with Green Sandpiper being the most likely species. Snipe and probably Jack Snipe winter in the rank vegetation in the centre of the spit. Waders also sometimes turn up on the grassy islands in the northern half of Broadwater lake; these islands are especially favoured by Lapwing and Oystercatcher.
Common Tern and Black-headed Gull breed on the rafts provided. Decent sized flocks of hirundines are often present over the lake. A good range of raptors can be seen, with Common Buzzard, Sparrowhawk, Kestrel, Hobby and Red Kite fairly regular. In addition Osprey and Peregrine were recorded last year.