A major river straddling the Aragón–Catalonia border and one of the Pyrenees' most important trout streams. Limestone throughout — alpine karst headwaters transition to dramatic canyon sections with crystal-clear freestone and technical pocket water. Strong wild brown trout genetics persist despite WFD 'Poor' ecological status (hydropower abstractions and flow regulation affect the middle reaches). Upper headwaters retain the best habitat. High altitude moderates summer temperatures. The Noguera de Tor enters through the UNESCO Vall de Boí. Access from Sort (Catalonia) or Beranuy (Aragón).
- Limestone