The Trinity watershed is a major tributary of the Klamath River that stretching nearly 3000 square miles through Trinity and Humboldt County. The watershed is almost entirely covered by mountains, falling within both the Klamath Mountains and the Coast Ranges. The Trinity River itself flows approximately 165 miles and is a Designated National Wild and Scenic River. Within the watershed Within the watershed, approximately 80% is federal land managed by the US Forest Service and the Bureau of Land Management. The remaining 20% is privately own, with about 10% by timber companies.
Overall, the Trinity watershed experiences a Mediterranean climate, with cooler, wet winters and hot, dry summers. Depending on the region, annual precipitation can range from 37 to 85 inches, with an average of around 57 inches. Oak, Fire, and Pine forests are the dominate land cover with small areas of chaparral and shrubs. The Trinity borders many drainage basins, including the Mad River, Salmon River, Scott River, Redwood Creek, Clear Creek, and Cottonwood Creek. Its steep, rugged terrain and large amounts of rainfall cause very fast runoff, resulting in flooding and high sediment content in the water.
The Trinity River is highly important for hydroelectric power, irrigation, fishing, and recreation. In 1961 the river was dammed, creating Trinity Lake which is the third largest lake in the state. For years mass amounts of water was diverted from the upper watershed for agriculture in the Central Valley. Environmental regulation enacted in 1991 required larger amounts of water be released, however the Trinity’s water is still in non-stop use.