Nearly all American estuaries have been seriously degraded by development, but South Slough's 4,500 acres of open water, marsh, mudflats and upland forest remain remarkably unspoiled. (A slough is a quiet arm of an estuary-an area near the mouth of a river where sea water mixes with freshwater.) These highly productive habitats teem with life, from clams and eelgrass to eagles and bears. Stop at the interpretive center to see the displays and to get maps showing hiking and canoe trails. If time permits only one hike, take the Estuary Study Trail, a 3mi series of loops that begins behind the center.