This paper describes a research project that has been conducted as part of the coastal habitat and management plans initiative (ChaMPs). The primary aim at this stage is to identify and quantify the salt marsh decline by mapping the changing extent of salt marsh coverage during the last 30 years. Rectified aerial images of the salt marsh were created for three epochs. The salt marsh and coastal boundaries were then mapped using a head-up digitising technique combined with stereo aerial photo interpretation. This methodology, though simple, provides an important estimate of salt marsh change for a number of harbours and estuaries in southern England. The results show a rapid decline in salt marsh habitat, with some areas showing a reduction of over half their existing salt marsh between 1971 to 2001. The authors consider the various theories that have been presented to account for this dramatic change and offer preliminary explanations. Though no doubt resulting from the combined effects of rising sea levels, Spartina dieback, restricted sediment supplies, pollution, and coastal squeeze, the authors underline the need for more detailed case studies of specific sites in the future.