Changing Temperatures in Rivers & Streams / Learning to Fish Rivers & Streams

The only constant in life… is change.

Yesterday, we took a look at some of the different water temperatures that fish prefer (with a focus on warmwater species). Today, we’re going to look at a range of elements that can have an impact on the temperature in a river or stream.

What’s a Good Way to Check the Water Temperature?

One tool that I keep with me whether I’m on foot fishing from the bank, or in a small boat, is my Deeper Pro+ Sonar. This is my preferred model because it allows me to check the temperature close to where I’m standing or on the opposite shore (if a cast can reach that far). It allows me to create and store my own topographic maps, it’s GPS enabled and syncs up with my phone to provide a depth finder & info on bottom composition:

What Causes Stream Water Temperature Changes?

Understanding what causes the temperature to change in rivers and streams can have a big impact on your fishing success. Take into consideration the time of year: in early spring for example, fish will typically be looking for areas with warmer water, but in midsummer, cooler water can be key. If you have the tools and the know-how to find pockets of cooler and warmer water, you can enjoy some spectacular fishing year round. Even a difference of just a few degrees can have a big impact on fish location.

The following pictures come from a book that my grandfather gave me a few years back titled The Freshwater Angler™: Fishing Rivers & Streams, but before we jump into that let’s quickly discuss temperature differences in the pool-riffle-run configuration we first explained while discussing current.

Fast-flowing water is completely churned and has less time to absorb sunlight. This means it will retain a cooler temperature longer, especially if the section in question is shaded from the sun. (Think riffles and certain faster-moving runs.)

Slow-moving water may also remain churned (remember river and streams do not normally stratify like a lake does), but slow-moving water has a longer time to soak up sunlight and heat. In especially slow-moving sections of a stream with no shade cover, the water can warm rapidly. (Think slower-moving runs and pools.)

Incoming Feeder Stream — Incoming feeder stream with cool, shaded, fast moving water.

This is why spring-fed tributaries are so important. These – along with other incoming sources of cooler water – are what allow streams to stay cool enough to maintain healthy populations of northern pike, walleye, or any fish that prefer (and thrives in) cooler temperatures. Without these, streams could only maintain a population of fish that could tolerate very high water temperatures – like largemouth bass, catfish or redbreast sunfish.

*Note: Some streams located in the north or in higher altitudes are not as susceptible to this because their summertime water temperatures remain moderate.

Key Areas to Look For

Narrow Shaded Portions of a Stream — Narrow, shaded portions of a stream will warm slowly because little water is exposed to direct sunlight.

Steep Fast Moving Stream Water — Steep sections within a stream with fast-flowing water will warm slowly because the moving water absorbs little heat.

Slow Moving Stream Areas Warm Faster — Flat portions of a stream with slower-moving water will warm faster (especially if there is no shade present) because the water has more time to absorb heat.

Surface Draw Dams Slow Water — Surface-draw dams spread out the water and slow the overall flow, which increases the stream temperature.

Incoming Springs Can Cool Stream Temperatures — Incoming springs can reduce the temperature of a stream in a small area below the entry point.

Flat Pools Warm Faster in the Sunlight — Wide, unshaded stream areas (like pools) warm rapidly because much of the water is exposed to the sun.

Cold Water Tributary — Coldwater tributaries (which are much larger than the incoming springs pictured above) cool a large area below the entry point.

Coldwater Draws Lower Water Temperature — Coldwater draws reduce the stream or river temperature by draining water from the ***cold depths*** of an upstream lake.

Moving Forward

Now that we understand what species of fish prefer what water temperatures, and the factors that can help determine that temperature in a stretch of river or stream, let’s look at some common food and forage options that these fish will be keyed in on. This will help when it comes time to select the right baits and presentations as we explore new streams this year.

Be calm. Be patient. Make it about them. — Be calm. Be patient. The more we learn… the more we can help them be successful.

Tight lines!

NEXT SECTION: Food & Forage
PREVIOUS SECTION: Preferred Temperature Ranges of Warmwater Gamefish

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