University researchers build machine to remove invasive waterweed

Researchers at the University of Oulu have developed a floating machine that removes Canadian waterweed from lakes and carries the plant to shore, Yle reports. The device can lift tonnes of the invasive species from the water, but is still being used only for research and is not available for purchase.

The machine was tested at Tulijärvi, a lake in Muhos, where cottage owners have battled Canadian waterweed for years. The plant has made boating, fishing and swimming difficult.

“We cottage owners are eagerly waiting to get a machine like this for our own use. It can reach places that cannot be reached by wading,” said Hannu Kärppä, deputy chair of the Rokua water protection association.

Rokua is a tourism and nature area covering parts of the municipalities of Muhos, Utajärvi and Vaala. The device has also been tested in Kuusamo.

Designed for narrow waterways

Canadian waterweed is an invasive species from North America that forms dense growths. It has been planted in aquariums and spread into nature with human assistance. The plant can reproduce from small fragments, making it difficult to eradicate.

Attempts to remove it include clearing with a seine, but the method is slow and laborious. Mowing is not recommended because it can spread the plant further.

The floating machine uses cutting blades, a collecting mechanism and a storage tank. Project researcher Jonne Untinen said similar machines exist elsewhere, but are considerably heavier in construction.

The University of Oulu’s machine was designed to be agile. Paddle wheels improve its movement among aquatic plants and prevent vegetation from becoming caught around a propeller. It weighs about 1,200 kilograms and can be transported on a trailer, including behind a van.

More than 10 tonnes in a working day

The machine cuts the waterweed down to the lakebed and lifts the plants onto a conveyor before they are placed in the storage tank. Untinen said it could remove more than 10 tonnes during a working day, including time spent moving between locations and unloading.

He said the machine can achieve a more thorough result than a seine. After seining at Tulijärvi, aquatic plants were still left on the lakebed at the depth of an oar blade.

The researchers hope the harvested waterweed can eventually be put to use. The biomass could be processed into biogas and fertiliser, but for now it mainly ends up as waste.