On Folsom Lake, Nature Finds a Way

An interesting thing is happening on Folsom lake this year- or should I say in Folsom lake. Along with a good number of feisty trout, we’ve been catching lots of small chinook salmon. Right now they’re between 10” and 14”, which would make them about a year old. 

Now, king salmon in Folsom lake are not unusual. Over the years, during spring, the California Dept of Fish and Wildlife has planted them there, as they do in several California reservoirs. Most recently in Folsom there were three consecutive plants: May of 2022, 2023 and 2024. They were put in in large numbers too: according to the Kokanee Power, a non-profit fishing group, 99,000 in 2022, 96,000 in 2023 and 125,000 in 2024. But that doesn’t mean there are 320,000 in the lake. They’re added in such large numbers because mortality rates are huge. Not only are they a perfect snack for predators like bass and birds, stocked fish- raised on pellets at hatchery- sometimes never learn to feed naturally and they starve to death. I couldn’t find a specific percentage for stocked chinook salmon, but for stocked trout mortality rates can be as high as 90%. And then of course, water conditions have to be good or, at least, good enough. Temperatures, oxygen levels, food chain health…it all adds up. And that, for a reservoir like Folsom- with its often-drastic seasonal shifts in water levels -can be a massive challenge. Remarkably though, enough tend to survive to give us a good fishery, and the last three years have been productive, with salmon reaching upwards of 8 pounds!

Last year, no chinook were stocked. A virus had been detected in the hatchery that provides the fish. To protect ocean-going stocks downstream, the Department of Fish and Wildlife erred on the side of caution. With most of the chinook planted in 2022 reaching the end of their life cycle last fall (some will live 4 years, most only 3), that means any salmon we catch this year will be from the classes of 2023 and 2024. And a lot of those have probably been caught too. The next couple seasons were looking a bit bleak.

BUT…the last few months have yielded a surprise, courtesy of Mother Nature. In January we suddenly started catching lots of little chinook. But with no recent plants, where are these fish coming from? This is where the story gets kind of cool.

Until about 2006, all chinook planted in Folsom lake were unsterilized. The belief was that whatever salmon weren’t caught would simply live out their life cycle in the lake. What biologists didn’t count on was that old adage: Nature Finds a Way. After the market crash of ‘08, budget cutbacks meant no salmon plants in Folsom for several years. But we kept catching them. The numbers weren’t huge, but they were still there. Where were they coming from? In the early teens, CDFW decided to check the south fork of the American river, which, along with the north fork, empties into Folsom. To their surprise, they witnessed spawning salmon as far upstream as Coloma. Fertile fish had established spawning runs. There were reports of spawning salmon on the north and middle forks, too. Naturally-hatched chinook were hanging in there - even in horrendous water years like 2014. Unsure how a naturally-propagating salmon population would affect those critical runs below the dam, CDFW biologists again opted for caution. When the chinook stocking program started back up in 2016, all fish, going forward, would be sterilized.

After the drought of 2014, then extremely heavy rains in 2017 and then another drought in the early 2020s- it was generally believed that whatever spawning runs there were in the river arms were probably finished. They were sort of looked at like a novelty anyway. I don’t think anyone really expected them to last long-term. Those of us who fish Folsom mostly stopped thinking about it…until this past January when, out of the blue, we started catching those aggressive little chinook. What was going on?

Well, 2024 and 2025 were exceptional water years. I’m no biologist (and I did reach out to the Department of Fish and Wildlife for help with this story, to no avail), but I don’t think it takes one to know these fish were naturally hatched. It makes sense we’re only seeing them now; a chinook salmon smolt will spend the first year of its life learning how to survive in the river of its birth. These little fish had done that and were now moving into their “ocean”- Folsom lake - for the next 2-3 years. We’re noticing them because their numbers seem quite healthy (wild fish: wilier fish) and with no plant last year, we’re not catching as many chinook overall. Happily, most anglers are releasing them, too. Hey, today’s 12 inch chinook is next summer’s 5 pounder. 

And that’s what amazes me about salmon in general: despite facing challenges that make a game of Oregon Trail seem like Mario Kart, they can survive. We saw it with our ocean-going fish this past year. We’re seeing it now in a mid-sized reservoir known more for big water level swings than for top-notch fishing. Nature. If given half a chance, she’ll find a way.