The Trinity River and many of its tributaries have been part of the National Wild and Scenic Rivers System since 1981. The main stem is designated from a point below Lewiston Dam to the confluence with the Klamath River. The North Fork and New River are designated from the boundary of the Trinity Alps Wilderness to the mouth, and the South Fork from State Route 36 to the mouth. A total of are classified as wild, as scenic and as recreational. The South Fork is the largest river in California without a single dam along its length. Although fish populations have declined since the early 1900s, fishing for salmon and steelhead has recovered on many parts of the river. The Trinity is known as one of the best steelhead streams in the western United States and is home to both wild and hatchery fish.: The California Office of Environmental Health Hazard Assessment (OEHHA) has developed a safe eating advisory for fish caught in the Trinity River based on levels of mercury or PCBs found in local species.