On a walking tour at Mono Lake, visitors get a stark introduction to 80-plus years of Los Angeles’ water use.

Interpretive signs stand among exposed tufa towers. They trace the lake’s decline, showing how much higher the water level is supposed to be under a 1994 decision.

LEE VINING, Calif. — At a trailhead surrounded by sagebrush, a naturalist welcomes a group of visitors to Mono Lake beside a sign that reads “Oasis in the Desert.”

Guide Ryan Garrett, his face alight, greets the group of vacationers and entreats them to see the value in the saline lake — it teems with migrating birds, it’s around a million years old, and it’s affected by water use in Southern California more than 300 miles away.

In the early 20th century, Los Angeles built a massive aqueduct to take water from the

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