Blagdon Lake is designated a Site of Special Scientific Interest (SSSI) of 212.7 hectares (526 acres), created in 1971, largely because of the variety of species and habitats. The area around the pumping station was laid out as an ornamental woodland which includes Scots pine, Cedar, Larch, Spruce, Oak, Beech, Chestnut, Willow, Lime, Holly and Maple. A variety of orchids including green-winged orchid (Anacamptis morio) and southern marsh-orchids can be seen on the borders of the lake.

A variety of water birds can be seen around the lake including: great crested grebe (Podiceps cristatus) and little grebe (Tachybaptus ruficollis), cormorant (Phalacrocoracidae), mute swan (Cygnus olor), Canada goose (Branta canadensis), duck (Anatidae), shoveller (Anas clypeata) and gadwall (Anas strepera). The common buzzard (Buteo buteo) can be seen on the surrounding hills and both Eurasian sparrowhawk (Accipiter nisus) and kestrel breed. Occasional visitors include: osprey (“Pandion haeliatis”), goshawk (Accipiter gentilis), Eurasian hobby (Falco subbuteo), nuthatch and great spotted woodpecker (Dendrocopos major). The ruddy darter dragonfly (Sympetrum sanguineum) can also be seen. In the wood at the western end of the lake there are populations of badgers, roe deer (Capreolus capreolus) and foxes.