varieties of invertebrates, angiosperms and fish. Chemical status, which compares the concentrations of various chemicals against known safe concentrations, is rated good or fail. The water quality of the River Foulness system was as follows in 2019. The upper river has not been classed as good quality because the dissolved oxygen content is poor, which may be due to faulty data. This also affects the lower river, where water quality is further reduced by poor management of nutrients, discharges from septic tanks and discharges from industry. The data for "Foulness from Black Beck to Market Weighton Canal" includes the channels of Black Dike, Foss Dyke, and the Market Weighton Canal above the junction with the Foulness. Like many rivers in the UK, the chemical status changed from good to fail in 2019, due to the presence of polybrominated diphenyl ethers (PBDE) and mercury compounds, neither of which had previously been included in the assessment. Natural history The majority of the area is agricultural farmland with large rectangular fields bounded by hedgerows, mainly composed of hawthorn but also including blackthorn, dog rose, elder and hazel. There are very few areas of woodland. Wildlife surveys of the river show evidence of European water vole, European otter, freshwater mussel and many amphibians. Water voles tend to inhabit the drains rather than the main river, although they do occasionally venture into it. Much of the farmland within the river catchment is registered as part of the Environmental Stewardship programme, which encourages good environmental practice in farming, with a significant proportion of that in the Higher Level Stewardship category. Within the Humberhead Levels, this scheme aims to increase populations of farmland birds, and to provide habitat for the breeding and over-wintering of wading birds. The scheme has been run in conjunction with the Royal Society for the Protection of Birds (RSPB) and the Yorkshire Wildlife Trust. The area is now noted for its red list farmyard birds, species which are at risk on a global, European or British level. Geology The river runs through an area where the underlying geology consists of Mercia Mudstone to the east and Sherwood Sandstone, dating from the Triassic period, to the west. This was largely covered by glacial deposits during the Devensian period, when most of the landscape was submerged beneath the waters of Lake Humber. Along the course of the river, more recent alluvial deposits are found. The