Malham Tarn

Limestone leaks, so standing water is rare in this country. An Ice Age glacier scoured down to impermeable slate, and clay and gravel sealed the outflow, leaving a lime-rich lake rather than the acidic tarns typical of upland Britain. It feeds the River Aire, and Stone Age campsites and tools have been found along the shore.

The tarn and the adjoining raised bog form a 147 hectare National Nature Reserve with SSSI, SAC and Ramsar status, managed by the National Trust. Habitats shift quickly from open water to fen, willow carr and rush pasture. Look for cranberry, bog rosemary, round-leaved sundew, bog asphodel, bogbean and ragged robin in the boggy ground.

Water birds may include great crested grebe, coot, moorhen, tufted duck and teal, while the surrounding wet grassland is breeding ground for snipe, redshank, curlew, lapwing and oystercatcher. Nothing is guaranteed, so bring binoculars and use the bird hide rather than expecting sightings from the track.

The main circular is considered suitable for wheelchairs and Trampers, which can be hired, though it is challenging: the first 500m is rough grass with gradients up to 1:10 before a surfaced track at least 3m wide. There is a wheelchair-accessible boardwalk loop at the Waterhouses end. Dogs are not allowed on the reserve boardwalk, and elsewhere should be under close control or on a lead near livestock.

• Open moorland weather turns fast, with wind and low cloud arriving with little warning; carry layers and waterproofs.
• Several sections are muddy and uneven after rain, and the gravel and unmade paths can be slow going.
• Approach roads are narrow, with gates and livestock to expect.
• This is a working reserve and estate, not a visitor centre with lakeshore facilities. A toilet sits near the Orchid House on the longer route, so plan accordingly.
• Treat the water as habitat rather than a place to enter.