The spit comprises a flint pebble structure around one mile long. Between it and the main shore is a salt marshy area with a wealth of wildlife and birds. The nearby Fawley Power Station discharged cooling water into the shallow waters around Calshot beach, and this has led to some reports of warm water species being attracted into the Solent. The Habitats Directive Review of Consents for the Solent Maritime Special Area of Conservation (SAC) did indeed identify thermal pollution on the intertidal zone on the west shore of Southampton Water, but this is likely to be from more than this one source. Excavation for the nearby power station discovered buried land surfaces from the Neolithic period.