Part of the National Trust’s Maidenhead and Cookham Commons, Cock Marsh is home to some of the most important ponds in the Thames Valley and indeed Southern England.

The ponds and surrounding grassland on Cock Marsh are home to an exceptionally diverse range of wetland and aquatic plants associated with pristine water quality and a long history of traditional management with grazing animals. A very special feature of Cock Marsh is that its floodplain ponds and wet grassland have been traditionally managed for many centuries: they have not been ploughed or artificially fertilised, and the grasslands have been continually grazed with relatively low numbers of cattle. This has enabled the native plants of wet floodplains to thrive, when they have been eliminated across so much of the English lowlands.

The four main ponds lie in a low area of grazing marsh, in a remnant channel of the River Thames, bordered to the south by a chalk escarpment which adds a subtle calcareous influence to the water chemistry. Whilst the site is entirely within the floodplain of the Thames, water quality tests have revealed that the ponds are particularly clean with barely a trace of nitrate or phosphate pollution.

The flora of the Cock Marsh ponds is outstanding, with many Red Data Book species present. Tubular Water-dropwort Oenanthe fistulosa, and Marsh Stitchwort Stellaria palustris, which are both Biodiversity Action Plan (BAP) species and categorised as Vulnerable in England, are doing well, along with nationally threatened Round-fruited Rush Juncus compressus and Marsh Arrowgrass Triglochin palustris. A range of wetland plants that are rare in Berkshire and surrounding counties such as Lesser Marshwort Apium inundatum, Fine-leaved Water-dropwort Oenanthe aquatica and Water Violet Hottonia palustris, are also present. Yet it is an even rarer plant, Brown Galingale Cyperus fuscus, recorded from only 12 sites in England, that makes Cock Marsh nationally significant. Our surveys recorded huge numbers of Brown Galingale plants– over 10,000. Brown Galingale populations can vary considerably year to year – but by any standard this makes Cock Marsh the most important site for the species in the UK – most other sites have recorded just a handful of plants in recent years.

Studying the Brown Galingale at Cock Marsh has shown us new ways to help manage it. It’s known that Brown Galingale needs bare damp ground to germinate in spring – at Cock Marsh, trees near to the ponds help create these conditions. Cattle shelter under the trees and their hooves disturb the wet ground near-by leaving muddy patches that are ideal for Brown Galingale. These findings show that it is vital not to cut trees back from some areas of the site. The trick of using trees to encourage cattle to disturb the ground could also help to manage Brown Galingale at other sites. In the summer some of the ponds dry up. This means that cattle go elsewhere to drink and graze – which may ensure that most Galingale plants can fruit and cast their seeds without being eaten. This shows how important it is not to deepen the ponds and make them into a permanent watering hole.