Rapid recession of glaciers and snowfields is threatening the habitats of cold-water biodiversity worldwide. In many ice-sourced headwaters of western North America, stoneflies in the genus Lednia (Plecoptera: Nemouridae) are prominent members of the invertebrate community. With a broad distribution in mountain streams and close ties to declining glacier cover, Lednia has emerged as a sentinel of climate change threats to high-elevation aquatic biodiversity. Lednia tumana, which is endemic to Glacier National Park, USA and the surrounding mountains, is the most well-studied species in the genus and in 2019 became federally protected under the U.S. Endangered Species Act (ESA) due to climate-induced loss of meltwater habitats. Three other Lednia species have also been described, and like L. tumana, each is endemic to a mountain region of western North America: Lednia sierra in the Sierra Nevada, Lednia borealis in the Cascade Range, and Lednia tetonica in the Teton Range. In this review, we provide a comprehensive overview of Lednia ecology, genetics, and physiology, with an emphasis on the conservation outlook for the group and species with similar headwater distributions. We highlight substantial progress made in the last decade to better understand the ecology and evolution of Lednia, including the identification of 140 Lednia-containing streams (an increase from 12 streams in 2010), and a more complete understanding of the degree to which warming streams may imperil species in the genus. In light of the ESA listing of L. tumana, we show that similar conservation threats likely face all extant Lednia species. However, substantial gaps in our knowledge remain, primarily centering around their distributions (and the potential for as yet undescribed species), life history, ecophysiology, and trophic ecology. We conclude by describing pressing questions for Lednia that when addressed will expand knowledge of the genus and its conservation as well as broader understanding of climate risks to mountain stream biodiversity worldwide.