Generally speaking, trout require very clean water to survive. That’s not to say the water always meets the general definition of “clean.” Trout can aptly handle muddy or dirty water after storms or during runoff. But, in terms of water quality, trout do, for the most part, require clean water.
When you think of trout, what are the images that pop into your head? Maybe it’s a crystal-clear mountain stream? A gorgeous alpine backdrop where melting snow gushes into a transparent creek? Or a tree-lined river coursing out of the mountains?
Trout live in some beautiful places. And they swim in cold, clean water. That’s the habitat in which they evolved. That’s the habitat they need.
How Clean is Clean?
Several years ago, while fishing Colorado’s Gunnison River in the middle of spring runoff, I was skeptical that I’d have any luck catching the river’s fabled brown trout. The water was high and muddy, and the weather was typically cold for that time of year.
But my guide for the day was certain that we’d catch fish. As he said to me: “Chris, just because the water is dirty doesn’t mean it’s dirty.”
The logic? Trout do, indeed, require cold, clean water to survive. But in most rivers, there are times during the year when rivers run high and muddy. And trout can do just fine in water like this.
Spring runoff, for instance, is part of the natural process. So, too, are storm events that muddy up normally clear rivers.
And, that afternoon, I had great luck fishing for the river’s big brown trout by drifting a San Juan Worm tight against the bank. The runoff had scoured some of the upstream river banks loose, and released naturally occurring earthworms into the muddy river. That’s why the worm pattern worked.
Dirty? Or Polluted?
While trout can handle “dirty” water, they don’t tend to thrive in water that’s polluted. Harmful chemicals, raw or poorly treated sewage, mining runoff or other contaminants are usually a death sentence for trout.
In fact, many scientists consider trout to be “indicator species.” If a river of stream can support trout, it likely means that it’s in pretty good shape.
And, what you might not realize, sometimes heat can be a form of pollution. An outflow from a power plant might inject warm water into a cold trout stream. That kind of “pollution” can be harmful to trout, too.
That said, there are some trout that have shown to have a tolerance for heavy-metal pollution (mining runoff). Some populations of brown trout seem to be able to handle pollution better than other trout species.
Now, of course, this isn’t ideal. Not for trout, and certainly not for us anglers. But, in a world where angling opportunities are diminishing, not increasing, it’s good to know that some polluted waters can still support trout.
How Can You Tell if a River is Polluted?
Around the world, regional governments do a very good job of monitoring water quality. Most known rivers that are polluted are known by local authorities. Simply checking with a local jurisdiction will tell you if water is clean enough for trout.
But you can also do the “eyeball test.” In mountainous regions, where mining activity is or once was common, it’s easy to see which rivers and streams are polluted.
If these waters turn yellow, orange or red after a big rain event, that means there’s a lot of heavy metals in the water. Zinc, arsenic, nickel, chromium and mercury are all byproducts of mining. These are common pollutants in rivers and streams that might otherwise support trout.
You can also help monitor trout rivers and streams for pollution. There are programs around the globe that can help you determine if your local river is healthy or if it’s suffering from pollution.
Almost all trout require very clean water in order to survive. Although some trout appear to be able to handle some heavy-metals pollution, that’s the exception, not the rule.
Trout can, though, happily deal with water that occasionally gets dirty. There’s a difference between dirty and polluted.
Trout streams all over the world will run muddy or silty now and then. Big storms or spring runoff can turn clear rivers into muddy ones. But the condition is temporary, and trout can tolerate periods of muddy or dirty water.
But chemical pollutants, sewage effluent and mining runoff that sometimes find their way into trout rivers can be deadly to fish.
Are Trout More Sensitive to Pollution Than Other Fish?
It seems so. Native and wild trout are definitely sensitive to pollution, and polluted water can wipe entire populations of trout.
What Fish Can Survive in Polluted Water?
In the United States, killfish, a native to the Atlantic Seaboard, thrive in water that contains 8,000 times the toxins that would be fatal to other fish. Other fish, like the common carp and the silver carp, can also handle water that is polluted.
Why Do Trout Need Clean Water?
Trout evolved in cold, clean water, often at the top of the world’s great river drainages, where pollution wasn’t present. For survival the require cleaner water than other fish to survive.
Can Trout Live in Murky Water?
Again, dirty and polluted aren’t the same thing. Trout can do very well in murky or dirty water. But pollution, like chemicals or effluent, can prove fatal.
Can You Still Catch Trout in Dirty Water?
Absolutely. In fact, fishing during high water when the rivers and streams are a bit dirty can be very good. Dirty water helps you disguise your presence, so your chances of catching trophy trout are even better.