Brown Trout Redds

The aspens are yellow, the mornings are frosty, and the Brown trout (Salmo trutta) are staging to spawn. Brown trout, like many of their salmonid cousins, migrate from lakes, oceans, or main-stem river reaches to headwater habitat to dig redds (nests in the gravel) and deposit their eggs­1. For Brown trout in the Upper Snake River region, many don’t have access to headwater habitat due to hydraulic barriers and will spawn in main-stem river reaches instead.

Brown trout can be particularly territorial and aggressive during spawning season, lending to great fishing opportunities if conditions are right. If you head out on the water this fall, please be cautious of where you wade. Trout eggs require high dissolved oxygen levels so female trout tend to build redds in pool-riffle transition zones where the water is 1-2 feet deep with substrate that is 0.5-2 inches in diameter2. If you wade in these areas, be cognizant of spots with disturbed substrate that look like the pictures below.

Best of luck fishing this fall and thanks for your cooperation!

Additional notes

We (HFF and IDFG) are still collecting data on gill lice in the Upper Snake River region. If you’d like to learn more about gill lice and how you can help, check out these links (gill lice update &  gill lice survey).

If you have questions, comments, or concerns, feel free to contact me at or 208-652-3567


1Groot, C., & Margolis, L. (1991). Pacific salmon life histories. UBC press.

2Louhi, P., Mäki‐Petäys, A., & Erkinaro, J. (2008). Spawning habitat of Atlantic salmon and brown trout: general criteria and intragravel factors.River Research and Applications24(3), 330-339.