Natural Floating Treatment Wetlands for Cleaner Water and Improved Habitat

This is guest blog post courtesy of our partners at the Methow Okanogan Beaver Project, enjoy!

by Julie Vanderwal, Project Manager, Methow Okanogan Beaver Project;

with contributions from David Grefrath

This Floating Treatment Wetland project is a collaboration between the Methow Okanogan Beaver Project and the Okanogan Conservation District, with funding through the Riparian Grant Program, a WA State Conservation Commission program funded by the Climate Commitment Act. Partners include Walking D Ranch, Moccasin Lake Ranch, the Methow Valley School District, including the Independent Learning Center and Liberty Bell High School, and Beaver Food Forest Farm.

Community designed structures float in temporary ponds while emergent vegetation becomes established

Why Floating Wetlands?

Floating wetlands can be installed to uptake excess nutrients in water, to create habitat complexity, for water bird nesting, to provide shade and refugia for fish, and/or to benefit many species of wildlife. Floating wetlands are also known as floating vegetation mats or floating vegetation islands, are being used all over the world, and have been featured in tens of thousands of research papers. Floating wetlands have been shown to improve water quality, particularly in areas affected by ranching, farming, or industry, and can enhance habitat in a variety of aquatic environments that would benefit from additional shade and structure.

Building structures that float and can physically hold plants in the water is a form of biomimicry for ecological restoration, similar to making beaver dam analogs that mimic natural beaver dams. If you look on the shores of lakes and ponds in our area and in wetlands, you may find natural floating vegetation that has formed with downed wood as a base, or as a result of a combination of plants growing together. These structures, including the roots of plants, are typically then colonized by microorganisms that contribute to buoyancy by producing gases and to nutrient uptake from the water, in the biofilm that develops as a community of bacteria, fungi, protozoa, and algae.

Methow Okanogan Beaver Project became interested in installing floating wetlands when a local project demonstrated high nutrient levels in pond water and chronic algae blooms over the past growing season. The team of practitioners and volunteers found that pond water at the Doran family’s Walking D Ranch had exceptionally high levels of total phosphorus, so they included floating wetlands in the project’s treatment plans, to help uptake excess nutrients. The red-winged blackbirds have also been utilizing the structures for perching over the water!

Practitioners discuss construction process

Why Natural Floating Wetlands?

A majority of floating wetlands in use today are constructed primarily of plastics, which leach volatile organic compounds, phthalates, and microplastics into aquatic systems during and after the life of their use. One of the most popular models available commercially is made from recycled PET plastic, injected with marine grade foam. Natural floating wetlands, though potentially shorter in lifespan, serve a similar ecological function, without releasing future pollutants into the environment. Natural floating wetlands have been constructed using various methods worldwide, but even these often include plastic capped pipes for buoyancy, and/or peat or coconut coir as a substrate. This project aims to eliminate the use of plastic in floating wetlands, as well as peat and coir, which each come with significant ecological cost.

Moccasin Lake Ranch Manager and assistant wave a floating wetland completely from coyote willow (Salix exigua)

Knowing it would be important to install natural structures, Julie Vanderwal, Twisp Uplands Ecological Restoration Project Manager, researched what others have done and reached out to community members and practitioners for ideas on how to design and build structures that would both a) support ecological health and b) foster responsible materials selection in the field of restoration. It also seemed clear that a 4x4’ platform could cost substantially less than the roughly $2,000 being charged for the popular comparable commercial product.

Using natural materials that are locally abundant, our community in Okanogan County has proven that there is a better way. These designs are innovations of local land stewards, high school students, restoration practitioners, and others who care about water and wildlife, who have gathered to contribute to the creative process. Like Elli Rosenthal, WDFW Habitat Biologist, said during one of the workshops, "It's like arts and crafts for adults who do restoration." Together, our community has developed 12 different designs this spring! These structures were planted with a mix of native emergent wetland plants, Juncus effusus (a rush), Scirpus microcarpus (a bulrush), and Carex species (sedges), and will be seeded in the fall with additional species, including native Typha latifolia cattails.

Independent learning center student hands floating wetland off to landowner representative Tom Doran for launching

Natural Floating Wetlands – An emergent field

Natural floating wetlands borrow the basic principles of industrial floating treatment wetlands, providing a buoyant structure for plants to grow hydroponically in place (in situ). Natural floating wetlands serve as a living laboratory for handmade designs using natural materials, including spent elderberry branches, birdhouse gourds, luffa gourds, cottonwood logs, and both flexible and rigid species of red osier dogwood and native willows. With a minimum of industrially produced materials (in some cases, none!), natural floating wetlands are regionally specific and spring forth from the communities who make them.

Structures built as part of this project have been launched at the Doran family’s Walking D Ranch, Moccasin Lake Ranch, and on private lands of Chris Smith, and Beth and John Sinclair. Some of the structures are being held in temporary ponds at Beaver Food Forest Farm near Twisp while the vegetation fully establishes, to see if this step improves outcomes.

While the structures made this spring have been placed in ponds, they can also be installed for habitat, shade, and water quality improvement in lakes, river side channels, and in pools where streams have been backed up and slowed down by beaver dam analogs. Floating wetlands can be anchored to remain in place, or allowed to drift to the shore, where certain plant species may establish roots in pond sediment, making the floating wetland a living part of the shoreline. The natural construction materials become especially important when the structures integrate into the ecosystem. 

The spring 2025 natural floating wetlands team is excited to monitor our structures, comparing structural longevity, plant survival, and buoyancy over time, so that we can determine which designs and processes to replicate throughout the region. 

To see some of these designs and how the process unfolded, visit the Floating Treatment Wetlands playlist on YouTube.

References:

Chance, et al, 2019. Short- and long-term dynamics of nutrient removal in floating treatment wetlands. Water Research, Vol. 159, pp. 153-163

Shahid et al, 2020. Role of Microorganisms in the Remediation of Wastewater in Floating Treatment Wetlands: A Review. Sustainability 12(14), 5559.

Shen, et al, 2021. Recent developments and applications of floating treatment wetlands for treating different source waters: a review. Environmental Science and Pollution Research. Vol. 28, pp 62061–62084

Urakawa, et al, 2017. The uniqueness and biogeochemical cycling of plant root microbial communities in a floating treatment wetland. Ecological Engineering, Vol. 108, pp. 573-580