By Elizabeth Nolan – Gulf Islands Driftwood
Published: October 11, 2011 7:00 PM
Updated: October 12, 2011 11:41 AM
Residents who draw their water directly from Cusheon Lake are being advised to drink bottled water following the discovery of a toxic algal growth.
Recent laboratory tests have indicated the presence of blue-green algae at the lake, with accompanying toxin levels above the acceptable limit in a raw water sample. Members of the Beddis Water Commission are now waiting for the results of a treated water sample, but according to consultant hydrologist Bob Watson, the existing treatment should be sufficient to filter out the microcystin toxin without adjusting chlorine levels.
“We’re monitoring it closely, but it should be fine without changes,” Watson said. “Our concern is with the homes with private intake on the lake. They shouldn’t be drinking the water unless they’re doing testing themselves.”
Watson said the Beddis Water Service will continue to monitor the situation each week. He is also trying to find more information for the lake’s private water users on which filtration systems can effectively remove the toxin, but noted, “Chlorine seems to be one of the few things that works.”
The Vancouver Island Health Authority issued a water advisory for Cusheon Lake late on Tuesday.
Testing at St. Mary Lake by the North Salt Spring Waterworks District has revealed the return of the blue-green algae to that water source as well, with toxins reaching the same levels they were at last spring.
This marks the first time the algae has been detected at Cusheon Lake, but Watson said this may be because testing has only been available for a few years. He added the cause of the bloom has not been determined but is interesting since Cusheon Lake and St. Mary Lake perform differently — the former has much more rapid intake and out-take, for example.
Customers of Salt Spring’s Highland Drinking Water System were advised not to use their tap water for drinking or food preparation because of the algal bloom in St. Mary Lake beginning Jan. 26, 2011. The addition of new sand filters at the Highland water treatment plant in March successfully filtered out the toxin, while NSSWD and Fernwood users were not affected because of the treatment system in place.