The Comau Fjord is an estuarine system in Northern Patagonia (42ºS), Chile: roughly 45 km long and nearly 490 m deep, with steep temperate-rainforest walls dropping straight into the water. High rainfall and snowmelt create a shallow brackish surface layer over a cold, saline body of modified Subantarctic water, producing steep vertical gradients in temperature, salinity, nutrients, and pH. The fjord region is difficult to reach and has almost no laboratory infrastructure — the Huinay Scientific Research Station is the exception that makes this work possible.