May 14, 2010, 7:33PM
Water clarity has improved at Blue Lake three years after Metro spent tens of thousands of dollars on algae-combating machines, but the devices may be abetting the spread of troublesome weeds.
“What we’ve found is that the pH has been a little bit worse, the water clarity has been a little bit better, and the toxic-algae problem has been about the same,” said Metro biologist Elaine Stewart.
The regional government and the solar-powered devices’ manufacturer say, however, that it’s still too early to render a verdict on whether the money was well spent.
Metro manages the popular 130-acre park on the lake’s north shore and cooperates with homeowners on the south shore over lake regulations. It split the $150,000 cost for the three SolarBee water circulation devices with the homeowners
“The lake was the clearest it had been in many years” last summer, said Sue Meyers, the immediate past president of the Interlachen Home Owners Association. The devices “seem to be working. We’re really happy with them.”
Due to its algae problem, which goes back decades, the lake is on the state’s list of waterways that fail to meet federal clean water standards. The blue-green algae blooms, which are usually worst in summer, can be toxic to humans and animals and create unsightly fouling of the lake near homes and docks.
In past decades, chemicals were dumped in the lake to beat back the algae, but the effectiveness was unclear, according to Metro. And it could have damaged the lake’s wildlife.
So in recent years, Metro and the homeowners began looking for a non-chemical solution. That led them to North Dakota-based SolarBee Inc.
The company makes floating, solar-powered units that circulate water in lakes and other bodies of water, disturbing stagnant water that’s well-suited for algae production.
Stagnant water is a particular problem at Blue Lake, which has no inlets or outlets. Instead, it is fed by groundwater, runoff and rainfall.
“We don’t eliminate blue-green algae, but in 90 to 95 percent of our applications, we see very clear success,” said Joseph Eilers, Northwest regional manger for SolarBee and a water quality scientist.
Mike Brown, a Metro employee who works with the homeowners, said he has heard positive things from residents about the SolarBees since they were installed in 2007.
But that’s come with some apparent tradeoffs.
A recent Metro report shows that last year the pH levels — an acidity measure — of water near the surface violated state water quality standards in nearly all of June, July and August.
And in October, the state issued a public health advisory because algae in the lake was the kind that can form toxins. The algae measurements exceeded the state’s threshold for issuing a health advisory a thousandfold, Metro said.
Mixing of the water by the SolarBees may have contributed to that, the Metro report said.“It’s a Catch-22,” Brown said.
Eilers said many lakes in Oregon experienced non-typical algae blooms in October. “The fall (bloom) appears to be an anomaly,” he said.
“Most people who live on a lake want the water quality to be best in the summer, when they have most of their contact with the lake. And if you look at the data for Blue Lake, that is indeed when water quality has improved the most,” Eilers said.
Another concern is whether the increased water clarity is increasing the growth of aquatic weeds by allowing sunlight to penetrate to greater depths.
Of particular concern is Eurasian milfoil, an invasive plant that can foul boat props and form thick mats. It was found at about three-fourths of test sites throughout the lake last year, six years after being found at only one site.
That plant growth, in turn, could have led to the increased pH levels in the lake.
“However, there is no clear evidence that any changes that occurred were verifiably caused by the SolarBees,” the Metro report cautions. Agency scientists in the past have noted alternating years of high algae growth and high aquatic plant growth.
“Management of Blue Lake may involve a trade-off between having abundant (aquatic plants), abundant algae or some level of both, but it cannot be expected to be a clear lake with low productivity,” the report cautions.