A large volume of water flows through the four mile-wide and almost fifty mile-long estuary of the Columbia River. As the river tumbles from the Cascade Mountains to sea level, it meets the ocean with tremendous force. Huge Pacific waves, some of the largest on the west coast, slam back. Ocean tides reach far up into the river estuary, creating a large area where fresh water mixes with salt.

The fragile estuary environment is dotted with islands and marshes. Local land use has changed the estuary, reshaping it with dikes, logging, agriculture, and urban development. Islands, pastures, and wetlands have disappeared, while new ones have formed or been created. Even so, a string of wildlife refuges retain some of its habitat. Partnerships of organizations and volunteers are working to restore more of its marshes and wetland.