September 29, 2025 — When she looks at the Narraguagus River, Valerie Ouellet sees what others can’t: a thermal mosaic that explains why it’s one of the last places in America where wild Atlantic salmon come to spawn.
This 55-mile-long waterway in Downeast Maine is a hodgepodge of cold-water pockets hidden within the warmer river where adult salmon can find refuge from the state’s increasingly hot summers.
Atlantic salmon do their best growing and spawning in 68-degree water. Any higher and they stop eating; they lay fewer, smaller eggs. At 73 degrees, they swim erratically. If they don’t find cold water created by shade trees, spring-fed tributaries or groundwater seepage, some will die.
Ouellet is an ecologist with the Atlantic Salmon Federation and is part of a state and federal research team that has spent two years documenting the river’s temperature and flow to explore how close, how big and how cold these spots must be for salmon to survive.