Fewer than 200 adult southern mountain yellow-legged frogs remain in their native California habitats today. This summer, the San Diego Zoo Wildlife Alliance did something extraordinary: they released more than 10,000 of them back into the mountains.

  • <200 adult southern mountain yellow-legged frogs (Rana muscosa) estimated remaining in the wild
  • 3,000+ frogs and tadpoles reintroduced into the San Bernardino and San Jacinto mountains in 2026
  • 10,000+ total individuals released across all California mountain habitats this year
  • 92% of the species' historic Sierra Nevada range is now empty of the frogs

From Showers of Frogs to the Edge of Extinction

It wasn't always like this. Mountain yellow-legged frogs were once so abundant in the Sierra Nevada that walking along a lake bank was difficult — the frogs covered the shoreline.

"These frogs used to be quite abundant. In the Sierra Nevada mountains, there are reports of showers of frogs jumping as scientists walked along a lake bank, and even of it being difficult to take a step without landing on a frog," said Dr. Talisin Hammond, a recovery ecology researcher at the San Diego Zoo Wildlife Alliance.

That world is gone. Introduced trout, the chytrid fungus, wildfire, and drought drove both mountain yellow-legged frog species — Rana muscosa (southern) and Rana sierrae (Sierra Nevada) — to IUCN Endangered status. The southern species has lost 92% of its historic range.

"It's hard to say when, exactly, this was last true. We know that throughout the species range, populations have been declining since the late 1960s and early 1970s." — Dr. Talisin Hammond, San Diego Zoo Wildlife Alliance

What 10,000 Frogs Looks Like

This year's reintroduction took place in the San Bernardino and San Jacinto mountain ranges — high-elevation habitats chosen for their capacity to support recovery. Teams waded into alpine lakes and gently encouraged tadpoles and young frogs out of clear transport containers, one careful step at a time.

One of the release sites is Bluff Lake in the Big Bear area — not far from a well-known bald eagle nesting site — illustrating how recovery ecology is reshaping entire mountain ecosystems, not just saving a single species. Conservation teams are monitoring health, survival rates, and breeding success at each release site throughout the season.

Dr. Hammond leads a core team of eight scientists at the zoo dedicated exclusively to the frog program. Their work spans captive breeding, reintroduction logistics, post-release monitoring, and disease management.

Twenty Years in the Making

The 2026 effort represents the culmination of two decades of conservation work. The San Diego Zoo Wildlife Alliance has maintained a captive-breeding program for these frogs for 20 years, steadily building the capacity to release thousands at a time. Partners including the National Park Service and California Department of Fish and Wildlife manage the broader recovery strategy — which also includes removing invasive trout from key Sierra Nevada lakes and treating the chytrid fungus that devastated populations in the 1980s and 1990s.

The goal isn't just survival — it's restoration to the scale where mountain yellow-legged frogs once again define the ecology of California's high-altitude lakes. At 10,000 released in a single season, that goal has never been closer.