Floating Treatment Wetlands

What’s that island?


The floating island in our storm water pond is what’s called a Floating Treatment Wetland (FTW). Cascade Meadow installed it in the summer of 2013 to both demonstrate an innovative new technology and to further improve the quality of the water that leaves the pond and enters our wetlands.

How does it work?

Floating Treatment Wetlands mimic some of the water-cleaning (or “treatment”) effects of natural wetlands, namely filtering and nutrient removal. The island is made from a fibrous mat or matrix of recycled plastic which is planted with a variety of appropriate native wetland plants. As the roots of the plants extend through the plastic matrix and into the water, both the roots and matrix become colonized by microorganisms or microbes. These microbes form a green slimy film (referred to as “biofilm” in the graphic below) on the roots and matting. As water flows through the roots and matting, the microbes take up various nutrients, such as phosphorus and nitrates, and filter out suspended solids.


What are the details of this particular project?IslandPic2

  • The island is 300 square feet in size and was made in a teardrop shape to echo the logo of Cascade Meadow.
  • The island moves up and down easily as water depth changes in the pond, which avoids issues with plants being flooded or drying out.
  • It was launched with a mix of over 600 plants including asters and sedges, swamp milkweed, ironweed and other wetland plants to build a filtering root system under the island and an aesthetic mix on top of the island.
  • A fence was added to discourage geese from disrupting the new plantings. The fence will be removed once the plants are established.
  • It was designed and installed by Midwest Floating Island, Heidi’s Lifestyle Gardens, and Sargent’s Gardens.


Want to know more?

Here are two detailed descriptions from “Floating Island International,” the holder of the patent on the technology:

“Floating islands have been demonstrated to remove all the typical wastewater parameters of concern – ammonium, nitrate, phosphorus, organic carbon and suspended solids — within a single island body.”

“The microbes and macrophytes uptake nutrients and move them into and through the food chain. Suspended organic particles stick to the biofilm and become periphyton, food for scuds, nymphs and ultimately fish. Suspended inorganic solids, such as heavy metals in particulate form, slough off and settle in the benthic zone beneath the island. The island is a sink for carbon dioxide and it enables nitrates and ammonia to be removed from the water and safely converted back to nitrogen gas.”

Want some really technical data?

Read the technical research paper documenting nutrient removal rates on Midwest Floating Island’s website.