Three Sites of Special Scientific Interest lie within the parish: Lewes Downs, Lewes Brooks and Southerham Works Pit. Lewes Downs is a site of biological interest, an isolated area of the South Downs. Lewes Brooks, also of biological importance, is part of the floodplain of the River Ouse, providing a habitat for many invertebrates such as water beetles and snails. Southerham Works Pit is of geological interest, a disused chalk pit displaying a wide variety of fossilised fish remains. The Railway Land nature reserve is on the east side of the town next to the Ouse, and contains an area of woodland and marshes, which now includes the Heart of Reeds, a sculpted reed bed designed by local land artist Chris Drury. The Winterbourne stream, a tributary of the Ouse, flows through it. This stream flows most winters and dries up in the summer, hence its name. It continues through Lewes going through the Grange Gardens and often travelling underground. The Heart of Reeds is one of the sites in East Sussex and Kent home to the marsh frog, an introduced species. It is popular with pond-dippers and walkers. A centre for the study of environmental change is due to be built at the entrance to the nature reserve.