Brook Trout | The Ultimate Bioindicators of Stream Health

The presence of brook trout says a lot about the condition of a lake, river, or stream. Brook trout are sensitive fish that can only spawn, grow, and survive in clean, cold water. If a body of water has a substantial brook trout population, it’s a sign that all is functioning as it should – and when those populations start to disappear, it’s often cause for concern.

Highly Sensitive Fish

Brook trout evolved in streams with cold, oxygen-rich water, and they haven’t adapted to withstand a wider range of conditions like some other trout species have. If a population begins to decline, it’s typically one of the first warning signs that a body of water is undergoing change.

Water Temperature

Brown and rainbow trout operate at their best in temperatures between 45° and 65°. Brook trout often get lumped into that ideal temperature range, but the reality is that any temperature above 60° begins to cause problems.

Coldwater ecosystems supporting trout are meant to stay cold – the organisms they support have evolved to depend on it. If brook trout are thriving in a body of water, it’s a good sign that water temps are right where they should be.

Oxygen Levels

Just like we need oxygen to breathe, all aquatic organisms need dissolved oxygen. Low oxygen levels affect every organism in a stream – from brook trout themselves to the insects they eat. If brook trout are growing to be big and healthy, it’s a clear indication that the ecosystem has enough oxygen to support its inhabitants.

Intact Habitat

For brook trout to spawn successfully, they need clean gravel beds, stable water flow, and limited sediment buildup—a strong brook trout population suggests that a body of water has these healthy qualities.

Easy Monitoring

Brook trout are territorial fish that typically don’t move far from their spawning grounds. Their tendency to stick in one place makes it relatively easy for researchers to monitor a specific population of brook trout over an extended period of time.

What’s Not to Love?

I have a real soft spot for brook trout – even if they didn't help us track environmental changes, they’d still be beautiful and fun to fish for. The next time you catch a brook trout, know what you have in your hand; they play a key role in our efforts to conserve trout habitat for future generations of anglers.