Big Reed Pond is a freshwater pond located in Montauk, New York on Long Island. A 128-acre (0.52 km2) site including the pond, brackish marshland and natural sand dunes was designated as a National Natural Landmark in 1973. The largely undeveloped pond is located within Theodore Roosevelt County Park. The Montaukett tribe lived in the vicinity of the pond until the mid-19th century. The pond and its associated wetlands are accessible via hiking trails that are open to the public.