What critical requirement forces the Wood Turtle's tight coupling to river systems for overwintering?

They require clean, oxygenated water for hibernation (brumation)

The Wood Turtle's semi-aquatic, riparian lifestyle imposes strict environmental constraints that drive its evolution and current habitat selection. A vital component of this is the requirement for overwintering, or brumation, which necessitates entering clean, oxygenated water. They achieve this by entering hibernation in the stream or river bottom, often utilizing soft substrate or hiding beneath submerged logs. This mandates a connection to flowing freshwater, meaning that the loss of high-quality stream corridors immediately compromises the population's ability to survive the winter, irrespective of summer foraging habitat quality.