Photo: File photo

Swimmers diving into Okanagan Lake at Kin Beach should prepare for a weedy experience.

The small, and rare, Rocky Mountain Ridged Mussel, which is native to the lake has complicated milfoil harvesting.

James Littley, with the Okanagan Basin Water Board, said milfoil rototilling will still take place at the popular Vernon beach, but in a more limited capacity.

Littley said there are new restrictions including not being able to rototil milfoil in depths less than 1.5 metres.

“If you think about the swimming area from the beach down to 1.5 metres at low water in the winter, and of course the water will be higher in the summer, we are probably looking at the first six feet of depth where we probably won't have been able to prevent the weeds from growing in the winter,” said Littley. “So in the summertime, that area we would expect would eventually become infested in the swimming area.”

Littley said they would be allowed to harvest in that area but “that would mean having our big harvesting machine in that area during the peak of swimming season.”

Harvesting will cut the weeds to a depth of five feet, but it does not prevent their regrowth.

There are only two harvesters on the lake and with the new restrictions it means they can only do one cut per area.

“Milfoil can grow up to five cm a day in the summertime,” he said. “So if we were to harvest at the beginning of July of the end of July, by the end of the summer we are going to have milfoil at the surface again. No matter when we harvest there in about a month you will end up with weeds at the surface.”

Last summer, the province banned all rototilling in the area, but officials then allowed harvesting with a depth restriction.

Eurasian watermilfoil is a rooted submersed plant inhabiting the shallow waters of lakes in British Columbia and other parts of North America. The species is said to have been introduced from Eurasia in the late nineteenth century, likely in ship ballast.

Milfoil is aggressive and once introduced to a waterbody will displace native aquatic vegetation in a couple of years. In the Okanagan, Eurasian watermilfoil was first identified in the Vernon Arm of Okanagan Lake in 1970. By 1974, the plant was well established in all of the mainstem lakes of the Okanagan.