| Rostherne Mere | |
| Location: | Cheshire |
| Coords: | 53.354°N -2.387°W |
| Basin Countries: | United Kingdom |
| Pushpin Map: | Cheshire |
| Area: | 48ha |
| Depth: | 30m (100feet) |
Rostherne Mere is a natural lake in Cheshire, England. It is the largest of the Cheshire meres with an area of and a maximum depth of .[1] [2] It lies north of Rostherne village and south of the M56 motorway. Because of its importance for wildlife, the lake, together with neighbouring areas of woodland and pasture, has been declared a national nature reserve, a Ramsar site and a Site of Special Scientific Interest covering .[3]
The lake lies on thick sedimentary deposits of glacial origin above marl and salt-beds.[4] It was probably formed by a combination of retreating glaciers creating a kettle hole and subsidence caused by the underlying rock salt dissolving away.[4] The lake is fertile and base-rich with high levels of phosphate, nitrate and ammonia.[4] Nutrient levels have risen as a result of inflow from surrounding farmland and streams and because of the droppings from large numbers of roosting birds.[3]
Large numbers of ducks winter on the lake including tufted duck, pochard, goldeneye, teal and wigeon.[2] Roosting birds include up to 10,000 black-headed gulls, 1000 common gulls and 300 cormorants.[2] Breeding birds include great crested grebe, reed warbler and sedge warbler, while lesser spotted woodpecker and little owl occur in the surrounding area.[2]
The reserve has a variety of butterfly species including white-letter hairstreak, purple hairstreak and common blue.[1] There are few invertebrates in the deeper parts of the lake but shallower areas are home to various gastropod molluscs and leeches.[4]
The lake lacks submerged vegetation but has floating beds of yellow water-lily and white water-lily.[4] Around the edge are areas of birch and willow and reedbeds with common reed, lesser reedmace and sweet flag.[3] The woodland consists mainly of oak and has patches of wood sorrel, yellow archangel and early purple orchid at ground level.[3]
According to legend, Rostherne Mere is the home of a mermaid, who can sometimes be heard ringing a sunken bell beneath the water.[5]