New islands help improve Riverside pond water quality

Tiny islands bobbing in the pond at Riverside Park have a big task of improving the murky water quality.

Native plants cover the islands with sprouted tuffs, and ducks and turtles have already taken to them as a prime resting spot.

Watershed Consulting of Missoula installed the BioHaven floating treatment wetland islands last week, which reduce water pollutants by replicating and concentrating the wetland processes.

Christine Brissette and Patrick Hurley with the firm spent two days assembling the islands along the shore before placing them into the pond.

“The idea is that they act like natural wetlands,” Brissette explained. “They mimic the process of a natural wetland island, but have extra surface area.”

The core of the island is a Brillo pad-like material made of recycled plastic bottles. Eventually the plants, chosen based upon what grows in the area and for aesthetics, will fill out making the island appear natural to the pond’s landscape.

The pond is used by the city of Whitefish to collect all of the stormwater for the downtown area. A dozen islands were placed in the pond in a mix of sizes at a cost of $14,500.

Whitefish Interim Public Works Director Karin Hilding said improvements to the pond have been discussed for several years as residents have complained about the quality of the pond water. The city is also looking at other possible treatments, including aeration of the pond and pretreatment of the water before it enters the pond, she noted.

The islands, while anchored to the pond bed, will be moveable so the city can adjust them as necessary. A group of islands were placed at both the inlet and outlet to maximize the amount of water that will pass through the islands.

The BioHaven islands improve water quality by mimicking and enhancing natural wetland processes. The microbial communities that inhabit the islands in the plant roots remove nutrients, heavy metals and suspended solids from the water.

Floating Island International, based in Shepherd, produces BioHaven islands. The product is the idea of Bruce Kania and has been installed for about 12 years in locations around Montana.

Brissette said the islands will take this season to mature and fill in, but by next summer they will be actively improving the water.

“There are many factors that contribute to how ‘clean’ the water looks from shore, so it’s difficult to say when the public will notice a difference,” she said. “We do know that these islands will be improving how clean the water actually is.”

Brissette said the Riverside pond mitigates the impact of stormwater entering the Whitefish River by allowing coarse sediments to settle out in the pond before the water is discharged. While the system is effective, it does little to impact the nutrients and fine sediments also present in most stormwater runoff, she noted.

“BioHaven floating islands enhance retention ponds by entrapping fine sediments and processing nutrients, further reducing the pollutants that eventually enter the river,” she said.  

The islands can remain over winter in the pond and can sustain brief periods of drought.

The city coordinated the project with the Whitefish Lake Institute and an advanced chemistry student from Whitefish High School will help study the water quality improvements to the pond.