The Spit/Causeway is a nature reserve at the mouth of the River Wandle. It is a small triangular site, only about 50 m long, and 20 m wide at its broadest. It was overgrown and inaccessible but a new footbridge over the river and recent renovation work has opened it up to the public.
It comprises retreated tidal terraces bisected by a wooden boardwalk. There are two small sparse areas of shrubs and an area of hard surfacing on which is sited a piece of public art, called Sail by Sophie Horton (2003).
Ecologically, three large white willow trees are the main focus of interest.