Due to the presence of endangered Rocky Mountain Ridged Mussels, rototilling milfoil is limited in some parts of Osoyoos Lake this year. (File photo)

By Vanessa Broadbent

Osoyoos Times

The Okanagan Basin Water Board (OBWB) has started its spring milfoil control program on Osoyoos Lake, but at the risk of harming an endangered species of mussel is rototilling fewer areas than usual.

Due to the presence of Rocky Mountain ridged mussels the provincial Ministry of Forests, Lands, Natural Resource Operations and Rural Development is limiting where the OBWB rototills milfoil throughout the Okanagan.

The mussels, native to the Okanagan and found as far north as Vernon, are unlike the invasive zebra and quagga mussels the OBWB is working to keep out of Okanagan water bodies.

The province is concerned that rototilling milfoil could upset the Rocky Mountain ridged mussels’ habitat, OBWB operations and grants manager James Littley said.

A study completed by the province in 2015 showed the presence of the mussels in Osoyoos Lake, but rototilling wasn’t restricted until the OBWB’s five-year permit expired this year.

Now the OBWB is waiting for the province to establish terms and conditions of its permit to control milfoil in Osoyoos Lake.

“We’re currently being restricted in any areas where they’ve found mussels,” Littley said.

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The mussels have mostly been found on the north end of Osoyoos Lake, west of where the Okanagan River enters the lake, along most of the west beach other than a 100-metre section of Willow Beach. Most of the Haynes Point peninsula is also affected.

“We’re working with the province to determine what this means in the long run,” Littley said.

In the summer, the OBWB will clear a boating navigation channel through the north end of the lake using a harvesting machine that cuts the top five to six feet and collects the weeds.

“Unfortunately this does nothing for the weed control long-term” said Littley.

The board is also pushing for more research to be done on how milfoil impacts the mussels. It’s working on a letter that will be sent to the provincial government.

Because thick amounts of the weed reduce the amount of oxygen at the bottom of the lake, it’s likely that the mussels can’t exist in thick milfoil beds and would benefit from rototilling, Littley said.

“We want them to do more research before they make these management decisions.”

Although the affected areas only make up a small portion of where milfoil control normally occurs, not rototilling will allow it to spread more quickly and become more difficult to manage, Littley said.

“We’re concerned that if the prohibitions stay in place as they are, and as more mussels are found, the prohibited areas may expand.”