They Dragged 140 Trees Into a Wisconsin Lake. Fish Production Nearly Doubled.

In the summer of 2018, a Wisconsin DNR crew dragged 140 full-sized trees into the shallows of a 92-acre lake in Vilas County and pushed them into the water along about a quarter of the littoral zone. That's the entire method. No fancy engineering, just full-sized trees put back into the water, the kind of structural habitat that gets degraded and lost across lake shorelines as residential and watershed development moves in. Researchers had already been monitoring fish there for several years before the trees went in, and they kept monitoring for six more after. The project just won the American Fisheries Society's Sport Fish Restoration Project Award, and the results explain why.

Nine Years on Sanford Lake

The lake is Sanford Lake, a low-productivity, oligotrophic lake in Vilas County. The Wisconsin DNR, led by fisheries research team leader Greg Sass, partnered with Dairymen's Inc. in 2015 to run pre-manipulation monitoring on the fish community from spring 2015 through spring 2018. That's the boring but essential part: you can't know what changed unless you measured the lake before you touched it. In summer 2018, crews added the 140 trees to roughly a quarter of the lake's littoral zone. Researchers Maxwel Wilkinson, Joseph Mrnak, Andrew Rypel, Stephanie Shaw, and Sass then tracked the fish community's biomass and production through 2024.

What Actually Changed

Fish community biomass and production both increased significantly after the trees went in. Total fish community production rose from about 3.6 kilograms per hectare per year before the trees to 8.2 kilograms per hectare per year after, more than double where it started. The biomass turnover rate, a measure of how fast the fish community replaces itself, climbed 25 percent. But most of that gain traces back to one fish: Bluegill drove the increase in both biomass and production more than any other species in the lake.

The Catch

Here's the part that matters if you're picturing trophy muskie stacked up on new wood: the higher trophic level fish, specifically muskellunge, smallmouth bass, and walleye, showed minimal short-term biomass or production response to the tree drop. Bluegill drove almost all of the gain. The researchers also frame this as a result from one lake, calling it broadly applicable to other low-productivity, oligotrophic north-temperate systems with degraded littoral habitat, which is a claim about where the finding should generalize, not proof that it does everywhere.

What This Means for Where You're Picking to Fish

I've never watched a DNR crew winch trees into a lake, so I can't tell you what that changes about a specific spot from personal experience. What I can tell you is that this lines up with something I already believed from 30-some years of fishing UP cabin water: wood in the lake holds fish, and it's not close. This study just puts hard numbers behind it and adds a wrinkle I hadn't thought about, that the payoff so far belongs almost entirely to bluegill, not the predators most anglers would drive out to chase.

Practically, that means new wood cover is a confirmed bet for bluegill and panfish. The study doesn't tell us whether bass, walleye, or muskie catch up around that same wood later on, only that they hadn't within this study's window. If you run a fish finder with side imaging, laid-down timber and blowdown along an undeveloped shoreline is still worth marking, especially if panfish are what you're after. This is one study on one lake, not a rule for every lake with wood in it, but it's a good reason to stop overlooking the ugly, brushy stretch of shoreline everyone else runs past on the way to open water.

Citation

Wilkinson, M. V., Mrnak, J. T., Rypel, A. L., Shaw, S. L., & Sass, G. G. (2026). Coarse woody habitat addition increases fish community production. Fisheries. https://doi.org/10.1093/fshmag/vuag002