Lakes, ponds and reservoirs habitat audit

Lakes, ponds and reservoirs include all areas of standing open water. Reservoirs, by definition, are artificially created water-bodies, some of which enclose a very large area of water. All of London's lakes are also likely to be artifacts resulting from the damming of streams to create water features in parks and other formal landscapes, or as a consequence of mineral extraction (sand and gravel pits). Some of London's ponds may have natural origins but most extant 'natural' ponds are likely to be former farm ponds or marl and clay pits. In more recent years many new ponds have been dug for aesthetic or nature conservation ponds in parks, gardens and amenity open spaces; many of these newer ponds have artificial liners as they do not naturally hold water.

Ponds, lakes and reservoirs make an important contribution to London's biodiversity. However, these habitats generally differ in their nature conservation interest.

Smaller water bodies tend to provide valuable habitat for amphibians such as common frog, palmate newt, great crested newt and many species of dragonfly. Where there are dense stands of emergent vegetation such as greater reedmace Typha latifolia, a diverse range of other invertebrates are supported, such as the hoverfly Parthelophilus versicolor, a soldier fly Odontomyia tigrina and the bulrush wainscot moth.

Larger water-bodies (lakes and reservoirs) are noted especially for their wildfowl. Most larger lakes in London will support species such as pochard and tufted duck, and where fish are present, cormorants are now regularly seen. Better quality waterbodies support additional species including gadwall, shoveler and great crested grebe. In winter the large reservoirs provide important feeding and roosting sites for wildfowl and they can hold huge numbers of the aforementioned species as well as many others. Although the numbers of birds utilising London's lakes and reservoirs declines during the summer months, many lakes and reservoirs have breeding common tern and, where there is dense emergent vegetation, reed warbler, water rail and mute swan. Lakes and reservoirs are also favoured feeding locations for house martin and sand martin.

The most apparent threats to all areas of standing water are direct loss (redundancy of reservoirs, infilling of ponds), pollution (especially nutrient enrichment) and conflicting use (many of London's larger water bodies have a recreational and/or water supply function).

Water bodies, whether ponds, lakes or reservoirs, are one of the most popular landscape features; there are few parks in London which do not contain a pond, lake or formal water feature. Likewise the larger lakes and reservoirs attract anglers, boating/sailing enthusiasts and bird-watchers. Consequently, the awareness-raising opportunities are huge.

Restoration of neglected ponds is a task that can be achieved with relatively little input. In many cases a few days of volunteer effort or a day with a earth-mover can restore ponds or create new ones. Ponds can also be restored or created during the alteration or modification of flood-defence works along rivers or as flood storage lagoons or balancing ponds in flood relief schemes. The Countryside Stewardship scheme and environmental awards provided by local authorities and others often highlight ponds as a habitat that could be restored or re-created in the landscape. Garden ponds are thought to be an important resource for amphibians and sound practical advice on construction and planting of garden ponds could dramatically increase the number of wildlife-friendly garden ponds. All new development schemes could be encouraged to include ponds (and other wetland habitats) as part of surface water and grey water drainage schemes.

New lakes can be created as the result of the restoration of mineral workings and many water-bodies of value for nature conservation have been created in the past as a result of flooding of gravel pits. Restoration techniques have been refined to allow for the creation of a wide range of habitats ranging from islands to reedbeds to nest sites for sand-martins.

Redundant reservoirs can be enhanced to create new and very valuable wildlife habitat. The transformation of Barn Elms reservoir into the Wetland Centre is a perhaps the most impressive example. Although this is unlikely to be repeated on quite the same scale, new wetland habitats can be created within redundant reservoirs, or a compromise can be effected where the reservoir can be used for recreation with appropriate restrictions to maintain existing nature conservation interest.

Management of the recreation/nature conservation conflict of the operational reservoirs is likely to be the main opportunity for further progress in the future.