Located in the middle reaches of the Medway River system, Ponhook Lake Nature Reserve provides important habitat protection for plants of a distinct species association known as Atlantic Coastal Plain Flora.

These plants were likely much more widespread following the last period of glaciation, but changing climatic conditions has reduced their range to a narrow band of the Atlantic seaboard and three disjunct population concentrations, including the southwestern interior of Nova Scotia.

Coastal plain plants are restricted to wet habitats (bogs and lake/stream margins) where extreme growing conditions such as high wave action, ice scour, water level fluctuation or low soil nutrient conditions allow tolerant coastal plain elements to have a competitive advantage. They are threatened throughout southwestern Nova Scotia by cottage and second home development, vehicle use on lakeshores, and a proliferation of recreational facilities, including resorts and campgrounds.

Ponhook Lake Nature Reserve is scattered across nearly fifty small islands and lakefront properties on Ponhook and Molega lakes. While small, these parcels provide a refuge for at least eight significant coastal plain species, six of which are nationally rare.

Designated in 1992, this site is one of the oldest nature reserves in Nova Scotia. It was expanded from about 43 hectares to just over 200 hectares in 2023.