Sylvia Olive Pleadwell Sayer, Lady Sayer, was a passionate conservationist and environmental campaigner on behalf of Dartmoor, an area of mostly granite moorland in Devon in the south-west of England. She was chairman of the Dartmoor Preservation Association from 1951 to 1973, and remained deeply involved with the organisation until her death.

Dartmoor is an upland area in southern Devon, South West England. The moorland and surrounding land has been protected by National Park status since 1951. Dartmoor National Park covers 954 km2 (368 sq mi).