When Do Brown Trout Spawn?

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Brown trout getting ready to lay eggs in tiny stream.

Brown trout spawn in the fall. As the temperatures drop in September or October, brown trout get ready to lay eggs, fertilize them, and keep them safe. The fall means cool water temperatures, consistent flows, and ideal egg incubating conditions. While the exact day varies yearly, it always happens in the fall.

From start to finish, the brown trout spawn is a several-month-long process. All the factors that must align for a successful spawn are mind-blowing. Brown trout power through the spawn and survive to see their eggs hatch. It takes a toll on brown trout, but they have enough energy to withstand the lack of food and hard work to complete the process.

Brown Trout Spawn 

In the northern hemisphere, you’ll find that most brown trout spawn around the same time. Trout’s bodies and water conditions align to start the spawn when the leaves change color. The brown trout spawn is one of my favorite times of the year.

When Do Brown Trout Spawn in Michigan

In Michigan, brown trout start spawning in September or October. The spawn starts around September in the northern parts of the state, but the southern sections aren’t ready until October or early November.

When Do Brown Trout Spawn in Colorado

If brown trout spawn at high elevations, they’ll start spawning in late August or September. The cooler temperatures get things going faster than normal. At lower elevations, Colorado brown trout spawn around October.

When Do Brown Trout Spawn in Pennsylvania

Brown trout don’t start spawning in Pennsylvania until October. Some higher-elevation streams are ready earlier, but October is the prime month for brown trout spawning in Pennsylvania.

When Do Brown Trout Spawn in Montana

Similar to Colorado, brown trout spawn at different times in Montana. Brown trout sitting at high elevations start spawning in September. Lower-elevation brown trout spawn in late September or October.

When Do Brown Trout Spawn in Wisconsin

Late September and October are the prime brown trout spawn months in Wisconsin. Air temperatures drop quickly, and water temperatures aren’t far behind.

Brown trout preparing for the spawn in the water.
Brown trout preparing for the spawn.

How Brown Trout Spawn

Brown trout need various things to fall into place before they can spawn. The environment and their bodies must be ready so everything can go smoothly. Males and females have very different roles during the spawn. 

Males and Females

For the spawn, the males are in charge of fertilizing and protecting the eggs. 

The females are responsible for digging the nest (redds) and laying the eggs. Their nests are the small holes in the gravel where females lay their eggs. The holes protect the eggs from getting swept into the current and forced downstream. 

Females want their nest to be in a place with good water flow because it’s the coldest and most oxygenated water. Females lay on their sides and flex their bodies to dig the holes. 

Once females dig the redds, they get ready to lay their eggs. Males fight over females and try to be in the right place as soon as she’s prepared to lay. She’ll lay her eggs, and the males fertilize them simultaneously. As soon as females lay the eggs, they dig more gravel to try and cover the eggs with it. 

The eggs take anywhere from 60-100 days to hatch. 

Danny's hand holding the South Dakota Brown Trout pointing to the river.
South Dakota Brown Trout

Water Conditions

For the spawn to run smoothly, water conditions must be ideal. When the trout are satisfied with the water conditions, they’ll start the spawn.


Brown trout want water temperatures in the 40s and 50s. Since they spawn in the fall, trout sometimes have to wait longer to get the spawn going if it’s an especially warm year. The colder water helps trout stay active and incubates the eggs better.

If the main river or stream fluctuates water temperature, brown trout move into small tributaries to find consistent flows and temperatures. They’re particular about what they want. 


Most brown trout spawn in water that’s less than five feet deep. As long as the water has consistent flow and is highly oxygenated, shallow water is okay. In shallow water, the current is easier for trout to maneuver.


Current is vital for brown trout. Consistent flows help oxygenate the eggs and make all trout’s lives easier. Flows somewhere around 100 CFS are ideal for brown trout.

River Bottom

Wherever trout spawn, they want to have a gravel bottom. It’s easy for females to dig into, and the eggs are stored well within it. Gravel keeps eggs lodged.

When fishing during the spawn, do your best to avoid the redds. If you step into a redd, you can kill thousands of eggs, so be careful in your travels during the fall.

Close-up pic of brown trout (Salmo trutta) getting ready to lay eggs in a creek.

Where Brown Trout Spawn

Brown trout return to the same general location every year to spawn. They swim from lakes into rivers or a certain part of the river into another. They know the conditions they want and rarely settle for anything less than perfect. 

Where one brown trout spawns, you’ll likely see numerous others. The spawn is a compact and crowded process. 


North of the equator, the brown trout spawn occurs in the fall. Brown trout spend all summer fattening up for the spawn. It’s exhausting, and sexually mature fish eat little while the spawn is occurring. Come September and October, the spawn gets going, and the eggs won’t hatch until around the new year, depending on water conditions.

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