Why Do Trout Swim Upstream? The Spawning Run Explained 

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Close up image of rainbow trout's head above the water.

Trout are migratory fish. They swim upstream from big-water habitat into smaller, calmer waters when it comes time to spawn. Some species of trout, like rainbow trout and cutthroat trout, migrate and spawn in the spring. Other species, like brown trout, swim upstream and spawn in the fall.

When I was a beginning fly fisher some 30 years ago, and living in the mountains of central Colorado, I remember stumbling upon one of the coolest things I’d ever seen

It was October, and it was unseasonably warm. I followed a blue line on the map well into the mountains along the Continental Divide. There, in a meadow a good 20 miles off the pavement, I came across one of the most idyllic little trout streams I’d ever seen. 

Expecting it to be full of six-inch brook trout, I was surprised when I got to the water and noticed a long, foot-deep run of the creek absolutely full of migrating brown trout getting ready to spawn. And not small brown trout, either. They were big fish for such small water. 

At the time, my knowledge of trout biology was a bit limited. I didn’t know that trout migrated to spawn. But, just like every other salmonid, when it comes time to mate, trout run upstream to their natal waters, pair up and reproduce. 

Mesmerized, I watched the big trout for about an hour. They had likely moved up the creek from a lake about 10 miles downstream. The females swept their big tails over the fine gravel, clearing out nests where they would eventually lay their eggs. The males jostled with one another for position. 

After the eggs are deposited in the gravel by females, the male trout will spray milt containing sperm over the eggs, fertilizing them. 

I decided not to fish that day, although I’m sure I could have done very well, especially seeing how aggressive the big, kype-jawed males were. It just didn’t feel right. 

And, over time, I learned that fishing for spawning trout, particularly when they are on the nests (which are called “redds”) is frowned upon. 

The Great Migration

Trout in the middle of the creek.
Can you see the migrating rainbow trout in the middle of the creek?

If you’ve ever watched a nature documentary on salmon — and who among us hasn’t? — you know that salmon swim from the ocean upstream into rivers every year to spawn. After they spawn, many salmon die.

But for Atlantic salmon and all species of trout, the annual spawning run isn’t necessarily a death sentence. Trout, especially, can spawn multiple times. And that means they swim upstream to mate and then back downstream when they’re done. 

While some subspecies of trout, like steelhead or sea-run brown trout, swim upstream from the ocean, most trout simply swim upstream from their normal habitat into the waters where they were born. 

Like salmon, trout “imprint” on their natal waters. This allows them to return every year to the same stream where they hatched from eggs buried in the spawning gravel. 

Just like their parents, they’ll find good spawning gravel, clean off a redd and make baby trout. If you’re lucky, you can be there to see it happen. 

All About Timing

Man wearing a cap holding the trout fish with both hands.
Brook trout and brown trout spawn in the fall. Rainbows and cutthroats run upstream in the spring.

Brook trout and brown trout spawn in the fall. Rainbows and cutthroats run upstream in the spring.

Not all trout spawn at the same time. For instance, rainbow trout and cutthroat trout are spring spawners. Brown trout and most char species, like brook trout, spawn in the fall.

Steelhead and sea trout run upstream from the ocean in waves over months. This is nature’s way of ensuring that if one spawning run fails, there will be another one on its heels. 

For inland trout in the Northern Hemisphere, the upstream spawning run for rainbows and cutthroats usually starts in March and April, with actual mating taking place sometime in May or June. 

Brown trout will start running upstream when water temperatures start to cool in September, and they usually mate in October. 

It’s Not All About Spawning

For some trout, the upstream “run” isn’t just about spawning. For instance, in Alaska, many wild rainbow trout spend their winters in lakes. When the ice melts, they move upstream to find food

And they’re joined in their upstream runs by Dolly Varden and sometimes even lake trout. After a long, cold winter under the ice all these fish are hungry, and they are on the prowl for food.

So, sometimes, the run upstream isn’t about spawning at all. It’s about finding a meal, first. The spawn requires a lot of energy, and the trout will need to put away some calories before mating.

Also, one important note. Trout will generally face upstream into the current. This doesn’t mean they’re migrating. It’s just easier for trout to breathe with water running over their gills

Fishing the Upstream Run?

Close image of man's hand holding a trout fish and a net.
It’s fine to fish the upstream run. But, when you see fish actively spawning, it’s time to put the rod away.

I don’t bother trout when they are actively spawning. And you shouldn’t either. All trout and char, during the spawning season, are aggressive. They’re either guarding redds or trying to keep other fish away from potentially fertile females.

For this reason, they’ll actively hit a lure or a fly. But, because when they’re in the throes of the spawn, they’re not really eating. They’re striking out of aggression. 

When you see spawning trout actively on redds, put your rod and enjoy the show. It’s rare to get the chance to see wild trout working to make the next generation of fish. 

How can you tell the fish are spawning? If the water is clear, you can see it happen before your very eyes. If the water is murky, the presence of trout leaping from the water is a good clue. 

Final Thoughts

Trout above the shallow water.
Brook trout really “color up” as they swim upstream to spawn in the fall.

Generally speaking, the motivation for trout running upstream is reproduction. In some places, trout run out of lakes into open water in search of food. But, in the end, the need to spawn is the reason most trout run upstream. 

Different trout run upstream at different times of the year. Rainbow trout and cutthroat trout migrate upstream in the spring. Brown trout and most species of char migrate in the late summer or early fall. 

If you see spawning trout, it’s best to leave them be. For many in the angling community, fishing for spawning trout is bad form. I prefer letting spawning trout do their thing, knowing that they’re busy making the next generation of fish for me to catch one day. 


Do All Trout Swim Upstream?

Generally, yes, but some trout will actually swim downstream to spawn. Take the cutthroat trout in Yellowstone Lake in Yellowstone National Park. Some of the native fish from the lake often run downstream in the Yellowstone River to spawn in gravel of the river. Others run upstream into one of dozens of spawning tributaries. 

Why Do Trout Travel Upstream?

Most trout migrate upstream into rivers and streams to find suitable gravel for spawning. But some trout and char, when ice melts in late winter, will run upstream to seek food. 

What Time of Year Do Trout Go Upstream?

It’s different for different types of trout. For instance, brown trout and brook trout run upstream in the fall to spawn. Rainbow trout and cutthroat trout run upstream in the spring. 

Why Do Trout Live in Streams?

Not all trout spend their entire lives in streams. Many spend winters sheltering deep in lakes, and migrate into rivers and streams in the spring, summer and fall to find food or good spawning habitat. 

Chris Hunt Avatar


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