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Experts will wade into Diamond Lake muddle

ROSEBURG ' State and federal managers Monday will begin testing whether they can bubble some of the water-quality troubles out of Diamond Lake, where summer water conditions have proven toxic to fish and people.

A lake expert from Bend will drop a 3&

189; -foot-wide aerator to the lake's bottom to test whether churning and oxygenating the water could be effective in combating vast mats of toxic blue-green algae called anabaena.

The anabaena, which have blossomed in part because the lake's regular food chain has been decimated by an explosion of illegally introduced tui chubs, triggered a three-week ban on swimming and wading at the eastern Douglas County lake.

Lake managers lifted the ban late Wednesday when the algae bloom dissipated.Hopes are that Monday's experiment will show promise for mass aeration to lower the lake's summer water temperatures and circulate the water to reduce the toxic algae much like tiny pumps keep aquariums healthy.

You know what to do when your aquarium's dirty ' you clean it out, said James Caplan, supervisor of the Umpqua National Forest, which includes Diamond Lake. But it's not that simple when it comes to something as big as Diamond Lake.

We need to find out if the bubbling will keep those toxic mats from forming, Caplan said.

Monday's study, however, will not answer that question as well as it might have because the algae bloom dissipated this past week.

Toxin levels in the lake were low enough Thursday for Forest Service officials to welcome wading anglers and swimming dogs.

The study initially was to test whether the aerator would cause the toxic algae to die or lose the battle for space with less-troublesome algae.

But now it will look just at whether it can churn and bubble the water without stirring up so much sediment that it causes more problems than it resolves.

Diamond Lake's long list of woes began when non-native tui chubs were illegally reintroduced there in 1992. The chubs have since ballooned to more than 30 million, eating the lake's zooplankton and squeezing out the trout stocked for anglers.

With zooplankton numbers down, the blue-green algae explode under the summer sun and release enough toxins to render the lake a health hazard to humans and pets. Cool weather kills the algae, and the lake's historic blue hue returns.

On Monday, lake specialist Joe Eilers will lower an aerator into various parts of the lake, either resting it on the bottom or suspending it atop the lake bed on a set of stilts.

Scientists hope thepulsating air bubbles will create a slow-moving current that circulates the water, allowing nontoxic algae to out-compete toxic algae.

Eilers said Monday's study won't determine whether aeration is the cure, just whether it shows promise.

We won't know the rest of the story, Eilers said. But at least the agencies will have an idea whether it's even feasible, on a physical basis, to go with aeration at Diamond (Lake).

The rest of the study, which will cost the Umpqua Forest about &

36;30,000, will be completed later this summer if the blue-green algae returns or be finished during next summer's expected algae bloom, Caplan said.

It's taken quite a while for the lake to get to the condition it's in, Caplan said. It may take active management for a few years to make this a fishable and swimmable lake again.

Reach reporter Mark Freeman at 776-4470, or e-mail