The San Joaquin River is Californias second-largest river. Its confluence with the Sacramento River in the San Francisco Bay-Delta creates the largest estuary on the west coast of the Americas and is a vital habitat for various fish species. Additionally, the San Joaquin and the Delta provide drinking water to 23 million Californians. However, the San Joaquin River and its tributaries are extensively dammed, with water diversions removing up to 70% of the rivers natural flow. As a result, more than 100 miles of the river have been dried for over half a century. The San Joaquin is also one of the most polluted rivers in the United States. It contains dangerously high levels of toxic pollution. In the 1980s, toxic selenium runoff caused a devastating wildlife tragedy at the nearby Kesterson National Wildlife Refuge.