Do know that most trout don't like to feed in water that is colder than 50°F? Or that in warm water they stick to the riffles because the heat drives oxygen out of still water.

The Umpqua Stream Thermometer will tell you if the water is ready for a hatch, too cold for feeding, or just right. It also helps you monitor rising water temperatures and make the right call on when to call it a day. Durable aluminum case, pocket clip and lanyard hole for easy carrying. Registers 20°F to 120°F