Beginning in 1930, more than 1.6 million fish were carried by horseback or dropped from aircraft into the naturally fishless mountain lakes of what is now Olympic National Park, creating recreational fishing opportunities in waters that had never supported fish populations before. Most lakes were stocked only once, although some were restocked repeatedly, with individual lakes receiving as many as 18 stocking events over the following decades. The introductions fundamentally changed ecosystems that had developed without fish predators, particularly for native amphibians that had evolved in these isolated mountain waters. Nearly a century later, researchers have completed the first comprehensive survey of fish and amphibian distributions across 117 remote lakes in and around Olympic National Park. Using environmental DNA, or eDNA, collected between 2019 and 2021, the team has now mapped where introduced fish remain and found that their presence is associated with lower detection rates for some native amphibians, while other species continue to coexist with fish by using habitats beyond their reach. The findings provide a clearer picture of how decades-old stocking decisions continue to shape these remote freshwater ecosystems today.
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