Lake Bottom Blankets (Benthic Barriers) in Wisconsin
As of September 2026: Benthic barriers are regulated under Wis. Admin. Code NR 109. This page summarizes current DNR guidance; confirm size and placement with your regional APM coordinator.
A benthic barrier, sometimes called a lake bottom blanket, is a mat laid over the lake bed to block light and physically prevent plants from growing underneath it. It's a physical method, not a chemical or a cutting one, but it's still regulated, and it doesn't fall under the same hand-tool exemption that covers pulling plants by hand.
How it works
Bottom barrier
About $0.20 to $1.25 per sq ft material; $10,000 to $20,000+ per acre installed
Kills a defined swim or dock zone; smothers native plants along with the nuisance ones.
Pros
- No chemicals
- Lasting control of a fixed area
Cons
- Needs a DNR permit
- Needs anchoring and periodic cleaning
Best fit: A set swim or dock area
A barrier suppresses whatever's growing under it, native and invasive plants alike, by cutting off light. It doesn't distinguish between species the way hand-pulling does, which is one reason the DNR treats it as a regulated installation rather than an exempt maintenance activity.
Why it needs a permit
Installing anything on the lake bed, even a fabric mat rather than a structure, is regulated under NR 109 and can also touch Wis. Stat. 30 depending on the placement. A barrier changes habitat under the footprint it covers for as long as it's down, affects bottom-dwelling organisms, and can shift if not anchored properly, so the DNR reviews size and location before you install one rather than treating it as equivalent to a rake or trimmer.
Size limits
Permitted barrier size is reviewed case by case against the specific waterbody and the area you need clear, typically scoped to a swim area or a boat lane rather than an open-ended footprint. There isn't a small-area exemption the way there is for hand-pulling, so even a modest mat at a single dock needs the same permit review as a larger installation. Check current size guidance with your regional APM coordinator before ordering material.
Cost and upkeep
Material runs roughly $0.20 to $1.25 per square foot, with installed cost landing higher once labor and anchoring are included, often in the $10,000 to $20,000-plus per acre range for a full installation. That's a bigger number than most owners expect for what looks like a simple mat, and it doesn't end at installation. Barriers accumulate sediment over time, which can eventually let plants root on top of the barrier itself, so periodic cleaning and eventual replacement are part of the real cost. Full comparison against other methods is on the cost guide.
When it's a good fit
A barrier makes the most sense for a small, defined area you want kept permanently clear, like a swim ladder or a boat slip, rather than a whole cove. For a lake-wide vegetation problem, mechanical harvesting or a coordinated herbicide program under an aquatic plant management plan usually makes more sense; see mechanical harvesting and how a lake-wide plan gets approved.
Because installation and permitting both take some expertise, most owners hire this out rather than DIY it; see what to ask a removal company.