Mason Neck National Wildlife Refuge was created to protect essential bald eagle nesting, feeding, and roosting habitats along the Potomac River. Along with active eagle nesting, the refuge hosts a rookery with more than 1200 nests for great blue herons. The 2276-acre refuge, in the Mason Neck State Park, contains about 2000 acres of hardwood forest, the largest freshwater marsh in Northern Virginia, and nearly six miles of shoreline.Visitors can view the refuge along two trails, one through woods and one in Great Marsh. In the spring, wildflowers fill the woods as songbirds migrate through the area and various types of ducks feed along the creeks and marsh. In the summer and fall, birds such as egrets and herons dominate the marshes before many of them travel south for the winter.From November to February, bald eagles breed and lay eggs.