At the beginning of the 20th century, Chislet Colliery was established by the Anglo-Westphalian Coal Syndicate, from where a layer of coal-bearing rocks beneath the valley was mined, which eventually caused subsidence of the surface above.

The presence of large water bodies and stands of reedbed, combined with the relaxation of grazing, created a haven for migratory birds and other wildlife.

[13] Interest in the natural history of the Stodmarsh valley was stimulated in 1947 by the field club of The King's School, Canterbury, which spent a year studying the site under the guidance of arts teacher David Stainer and biology master Cyril Ward.

In order to enhance the habitat for these birds, hundreds of hectares of reedbed was subsequently created on the flood meadows immediately east of the Lampen Wall in the 1980s and west of the Grove Ferry road in the 1990s.

Only a small proportion of the original grassland remains; the rest has suffered from gravel extraction, subsided into shallow lakes, been buried under mine waste or deliberately flooded and converted to reedbed.

[18] The grassland is nearly as ancient as the ditches, and is notable for its coastal character, with divided sedge Carex divisa, saltmarsh rush Juncus gerardii and narrow-leaved bird's-foot trefoil Lotus tenuis as typical constituents.

[21] In 2020 Natural England issued formal advice on nutrient neutrality in the Stour catchment,[22] in response to concern about the state of the SSSI.

The pollutants enrich the lakes, causing an algal bloom and fish die-off, threatening populations of protected birds and the wildlife of the SSSI in general.