[8] The frog occurs in mountain creeks, lakes and lakeshores, streams, and pools, preferring sunny areas.

It rarely strays far from water, and can remain underwater for a very long time, likely through cutaneous gas exchange.

Its breeding season begins once the highest meltwater flow is over, around March through May in the southern part of its range, and up to July in higher mountains to the north.

Fertilization is external, and the egg cluster is secured to vegetation in a current, or in still waters sometimes left floating free.

How long it takes for breeding onset varies from 1–4 years depending on the levels of snow and temperature.

When living in streams, it tends to eat terrestrial insects such as beetles, ants, bees, wasps, flies, and dragonflies.

[1] Its decline is attributed to many factors, including introduced species of fish such as trout, livestock grazing,[11] chytrid fungus,[12] and probably pesticides, drought, and ultraviolet radiation.

[13] Trout were introduced to lakes and streams throughout the Sierra Nevada in the late 1800s to increase recreational fishing in the area.

Some of the fish types that prey on tadpoles include the brown, golden, and rainbow trout, as well as the brook char.

The trout caused populations to isolate, restricted the amount of available habitats, and increased the chances of extinction.

[17][18] Frogs that have been reintroduced to water bodies cleared of fish have failed to survive, and analysis has isolated pesticides in their tissues.

[20] The relative roles that pesticides and introduced fish play in frog declines are still debated, and the loss of R. muscosa in its former range has probably been influenced by multiple factors.

[25] The first successful captive breeding of the frog occurred in 2009 when three tadpoles were reared at the San Diego Zoo.

Conservation workers at the zoo plan to release any more surviving captive-bred frogs in the San Jacinto Mountains, part of their native range.

[27] The Los Angeles Zoo is also a coalition partner and is raising two groups of wild collected tadpoles from two localities in the San Gabriel Mountains where they are released when ready.

[27][28] In 2015, the Oakland Zoo began a rehabilitation project of the frog in order to fuel efforts to save the species.

There, the tadpoles are grown to juvenile frogs, while also undergoing an inoculation process to render them immune to the chytridiomycosis fungus disease.

In 2016, the Oakland Zoo released 53 specimens into various lakes in Sequoia and Kings Canyon National Parks.

In 2021, the Aquarium of the Pacific partnered with government organizations like the California Department of Fish and Wildlife to create a facility for taking care of mountain yellow-legged frogs.

Following the wildfires, wildlife agencies found and moved these frogs into places like the facility established by the Aquarium of the Pacific.