Trout are cold-water fish. Depending upon which species of trout you examine, trout thrive in water temperatures ranging from the low-40s for brook trout up to the mid-50s for brown trout, with the rainbows, cutthroats, goldens and more exotic species falling in between. While optimum temperatures for trout cover only about a 15-degree range, they can survive in waters both colder and warmer than their preferred range.

It’s much the same as we humans. While we can survive in temperatures of 40 degrees below zero and in temperatures of 120 degrees above zero, we usually prefer temperatures between 60 and 90 degrees.

In the early spring, when the winter snow is just beginning to melt and stream temperatures are hovering around 40 degrees, fishing is more difficult, and you have to adjust your fishing tactics to catch fish successfully. Hot weather also requires adjustments in your fishing tactics if you want to catch fish.

Here’s a factor you need to commit firmly to memory if you want to catch trout in warmer weather: Warm water holds less oxygen than cold water.

Repeat after me: Warm water holds less oxygen than cold water.

Oxygen is just as critical for fish as it is for humans. I just visited a friend in an intensive-care ward at a local hospital, and right at the top of the monitor recording the patient’s vital signs was, guess what? A reading of the patient’s dissolved oxygen!

Fish in warmer water are just as stressed as a human during an asthma attack. They are concentrating on breathing, not on eating. To succeed in catching trout, you must find water with higher oxygen levels.

Here are some hints to increase your summertime trout success ratios.

Fish the colder waters. Now’s the time to fish those streams in the high country where there may still be some melting snow to keep water temperatures down. The higher-elevation streams (above 5,000 feet) are also more heavily forested, and the shade helps keep them cooler. Another great place to find cooler waters is the rivers below major dams. Water in lakes stratifies, and the water in the top layers of a lake is warmer than the water in the bottom layers. If you’re fishing the lake itself, fish the deeper waters. If you’re fishing the stream, then concentrate in the cold-water section below the dams. These cold waters below dams are often referred to as “tail-water fisheries” and sometimes produce monster fish.

Fish the tumbling waters, including the cascades, the rapids, the waterfalls and the deeper pools just below them. The physical action of rapids and cascades actually mixes oxygen from the air into the water. The higher oxygen levels resulting from cascades can offset (at least partly) the higher water temperatures. I have successfully caught trout from 70-degree water by concentrating on the cascade stretches where the rapids beat more oxygen into the water.

• Fish the spring creeks where water is fed into the stream by spring waters gushing in from underground springs. Big Springs on the Owens River is a perfect example of a spring creek stream. It’s pretty amazing to behold, as hundreds of springs simply gush out of the side of a mountain to form the headwaters of the Owens River. The water is so cold it makes your feet hurt, and the trout love it!

Warmer weather is surely a great time for water skiing, swimming and float trips down your local river, but it also presents some real challenges to the trout fisher. By using your head and applying some hot-weather trout tactics, you can overcome the challenges and have good trout fishing even in the heat of summer.

Until next week, tight lines.

• Don Moyer, outdoors columnist for the Tracy Press, has been writing Tight Lines for more than 30 years. His book, “Tight Lines: Observations of an Outdoor Philosopher,” is available online at www.createspace.com\3452025, and he will be doing book signings at local bookstores and libraries in the area. He can be reached at don.moyer@gmail.com.