The area around Castlemaine is of major ecological importance, with coastal habitats of excellent quality. Castlemaine Harbour is a very important site for wintering waterfowl providing good quality feeding and roosting habitats for an excellent diversity of waterbirds, including geese, waders, divers and seaduck. Species of birds found here include Brent geese, cormorants, shelduck, wigeon, dunlin, redshank, golden plover, oystercatcher. Part of this area is a Statutory Nature Reserve. it includes long stretches of river and stream which are excellent habitats for Salmon, Lamprey and Otter.
The protected natterjack toad is one of the rare animals found in the area.