The outflow that empties the lake into the Guadalupe River is at the very deepest point, so this supply of winter-stored water continues to chill the river, even in the middle of summer, with water temperatures that are close to those in February.

The Guadalupe River in Texas, particularly the section near Canyon Lake, remains exceptionally cold year-round because it is fed by the deep, bottom-level waters of the lake. When water is released from the Canyon Dam into the river, it is drawn from the "hypolimnion"—the deepest, coldest layer of the reservoir where the sun's heat cannot reach. This water is typically around 55°F to 60°F (13°C to 15°C), even in the middle of a 100-degree Texas summer. This "tailrace" effect makes the Upper Guadalupe a world-class trout fishery, as the cold, oxygen-rich water allows rainbow and brown trout to survive in a climate that would otherwise be far too hot for them. Further upstream, the river is fed by underground limestone springs from the Edwards Aquifer, which maintain a constant temperature of about 68°F. This combination of deep-reservoir releases and spring-fed headwaters ensures that the Guadalupe remains a refreshing, albeit brisk, destination for tubers and fly-fishers alike.