A distinct genetic heritage
The Chum salmon (Oncorhynchus keta) returning to the Namdaecheon River represent a unique and isolated branch of the species. Genetic analyses using mitochondrial DNA and microsatellite markers confirm that Korean chum salmon are a distinct population. They possess a lower genetic diversity compared to larger populations in Japan, Russia, and North America, but this has made their contribution to the overall species-level gene pool evolutionarily significant. This population marks the southernmost limit of the species' geographic distribution, having migrated through the waters off Russia and Alaska to reach the Korean Peninsula.
The life of a Namdaecheon salmon begins in the river's gravel beds. After hatching, the young fry spend only a few days or weeks in freshwater before migrating downstream to the ocean. They then spend three to five years maturing in the North Pacific, undertaking a migration that can cover nearly 20,000 kilometers. As adults, they are driven by a powerful homing instinct to return to the exact stream where they were born to spawn and then die, completing their life cycle. This philopatry, or natal homing, is what has kept the Namdaecheon population genetically isolated over millennia.
A population in peril
Historically, the Namdaecheon River supported a large salmon run, with over 70% of all salmon returning to Korea choosing this river. However, populations have seen a sharp decline over the last half-century. The reasons are multifaceted and common to salmon populations globally. Dam construction alters river flows and blocks migration routes. Logging and development along riverbanks increase water temperatures by removing shade and introduce silt that can smother eggs in the gravel redds. Water pollution and the effects of climate change, which warms both rivers and oceans, further stress the fish.
In response to the declining numbers, extensive restoration efforts are underway. The Yangyang Inland Fisheries Research Institute is central, operating hatchery programs that release millions of salmon fry into the river each year. More recently, Yangyang County has invested 28.2 billion KRW to construct Korea's first dedicated natural salmon spawning ground, set for completion in 2026. This 58,152-square-meter facility aims to create optimal, naturalistic conditions for salmon to spawn, potentially increasing survival rates from less than 10% in the wild. The facility will also feature an underground observation center for ecological tourism and education.