Cold-water fish like trout have a strategy for surviving extreme heat—moving into thermal refuges. Thermal refuges are areas in a river where colder water discharges into warmer stream water, creating a “cold-water patch.” This can be caused by groundwater seeping into the stream at specific locations or even when a smaller, well-shaded stream joins a larger river, creating a plume of colder water.

LINK (via Phys.org)