Draining the meltwater of Lago Argentino out toward the Atlantic, the Santa Cruz is a genuinely enormous river — glacial-blue, powerful and demanding, running through open steppe with a scale that dwarfs most Patagonian trout water. Brown and rainbow trout hold in its heavy current, and the river has also produced sea-run rainbows behaving remarkably like steelhead, most likely originating from escaped Pacific salmon-farm stock further along the coast — an unusual and still poorly understood wrinkle in an already singular fishery. Streamers fished with real weight, Woolly Buggers and Muddler Minnows worked deep and slow along seams and current breaks, suit the river's size and power far better than anything delicate. This is specialist expedition water, physically demanding to wade and best approached with local operators who understand its currents and access points. Big country, big river, fish built to match both.

• Glacial