Floating treatment wetlands turn existing retention and detention ponds into active nutrient removal systems. Meet MS4, TMDL, and nutrient reduction mandates with proven, low-maintenance infrastructure.
Stormwater programs face an impossible equation: stricter nutrient limits, aging infrastructure, no new land, and less money every year. Traditional BMPs like constructed wetlands or wet ponds require significant footprint and ongoing maintenance. Chemical treatment works but creates dependency and recurring cost.
Floating treatment wetlands offer a third path. They retrofit directly into your existing stormwater ponds, converting passive detention basins into active treatment systems without expanding your footprint by a single square foot.
Source: Compiled field-scale data from 11 international FTW installations. See Performance Data for full citations.
Install directly into existing retention ponds, detention basins, and stormwater facilities. Zero land acquisition, zero permitting for new construction.
No pumps, no electricity, no moving parts. Treatment is driven entirely by plant biology and microbial biofilm activity on submerged root systems.
Maryland provides an EIA credit equation for FTWs. NC DEQ awards SCM credit at 5%+ coverage. Florida DEP assigns a 12% treatment credit. The Chesapeake Bay Program Expert Panel defines formal nutrient removal rates at 10-50% coverage. FTWs are an accepted stormwater BMP in a growing number of jurisdictions.
Compared to ongoing chemical treatment, floating wetlands typically break even within 4-13 years. After that, treatment is essentially free with minimal annual maintenance.
At just 5-10% surface coverage, floating treatment wetlands convert a passive detention basin into an active nutrient removal system, and they become more effective each year as root systems and biofilm communities mature.
MS4 compliance: Retrofit existing stormwater ponds to demonstrate pollutant load reduction for permit renewals. Document BMP installation and performance for annual reporting.
TMDL implementation: Floating wetlands provide measurable nitrogen and phosphorus reduction that counts toward Total Maximum Daily Load allocations for impaired waterways.
Green infrastructure credits: FTWs qualify as green infrastructure in many jurisdictions, providing dual credit for stormwater management and habitat enhancement.
Phased deployment: Start with a pilot installation in one pond. Measure performance. Scale based on results. The modular system means you can add coverage incrementally as budgets allow.
Our sizing calculator estimates module requirements based on your pond dimensions and treatment goals. For large-scale municipal projects, contact us directly for engineered specifications and volume pricing.
Floating treatment wetlands are gaining formal recognition as an approved stormwater best management practice. The strongest regulatory pathways exist in these jurisdictions:
MDE lists FTWs as an "alternative BMP" in the 2020 MS4 Accounting Guidance with a specific equation (Equation 6) for calculating EIA credit. MS4 jurisdictions report TN, TP, and TSS load reductions from FTWs toward NPDES permit restoration requirements.
NC DEQ's Stormwater Control Measure Credit Document awards TN and TP credits for wet pond FTW retrofits at 5%+ surface coverage. FTWs are the "most common wet pond retrofit" in the state, with established effluent concentrations and runoff reduction values.
The 2016 Expert Panel report defines nutrient removal credits for FTWs across MD, VA, PA, DC, DE, WV, and NY. Recommends 10-50% coverage for increasing credit, with a net effect of 8-12% TN and 5-10% TP reduction. Three-year renewable credit with field inspection.
Florida DEP assigns a 12% treatment credit for FTWs toward watershed nutrient reduction goals. UCF research recommends 5% pond coverage for standard conditions, 10% with additional nutrient loads. Funded in part by EPA 319(h) Nonpoint Source Grants.
The EPA has not yet added FTWs to the National Menu of BMPs as a standalone category, but it does not preclude their use. The EPA actively participates in FTW research, co-convened the Chesapeake Bay Expert Panel, and has funded projects through 319(h) Nonpoint Source Grants. The BMP list is "not all-inclusive" and "does not preclude MS4s from using other technically sound practices."
900 m² of FTW at 5% pond coverage, deployed for 4 years (2016-2020). Harvested 1,927 kg of nitrogen and 384 kg of phosphorus from a eutrophic stormwater pond. Funded by an EPA 319(h) Nonpoint Source Grant and ongoing stormwater tax revenues.
Harris County Flood Control District tested and evaluated multiple FTW designs as "an additional cutting-edge approach to reduce stormwater pollutant loads in flood control facilities" across their watershed infrastructure.
Three-city pilot study (2016-2020) deploying FTWs for urban stormwater treatment. Chicago's Bubbly Creek installation used five islands totaling ~3,000 sq ft to clean a historically industrial stretch of the Chicago River.
Virginia Tech field demonstrations led by Dr. David Sample evaluated FTW capacity to enhance nutrient removal in wet retention ponds. Results inform the Virginia Technology Assessment Protocol pathway for BMP approval.
Additional municipal deployments include Billings, MT (174-acre stormwater drainage); Mississauga, Ontario (912 sq ft, Credit Valley Conservation Authority pilot); multiple sites across Orlando, Ruskin, and Gainesville, FL (UCF three-site study); and Lake Champlain Basin, VT (cold-climate stormwater evaluation).
FTWs are attractive to municipalities precisely because they retrofit into existing wet ponds, eliminating land acquisition, major construction, and storage capacity reduction.
No land costs: FTWs float in ponds you already own and maintain. No land acquisition, no easement negotiation, no new impervious surface.
Major savings vs. constructed wetlands: A Sunshine Coast, Queensland case study showed FTWs saved nearly $1 million compared to a conventional constructed wetland at the same site. The cost advantage comes from zero excavation, zero re-plumbing, and negligible opportunity costs.
Phased installation: Modular systems spread costs across fiscal years. Install 5% coverage in Year 1, expand to 10% in Year 3 as budgets allow. No need to front-load a massive capital project.
Funding pathways: EPA 319(h) Nonpoint Source Grants, state stormwater revolving funds, and green infrastructure grants all apply to FTW projects. Stormwater utility fees can fund ongoing operations.
"Finding means of improving wet pond water quality performance could represent an opportunity to provide real reductions in nutrient and sediment loads to receiving waters without requiring additional space. This would help municipal government achieve required TMDL reductions at lower costs." -- WEF Stormwater Report
Use our free calculator to size a pilot project, or contact us for engineered specifications and volume pricing.