The nearly four-month advisory against water contact at Lost Creek Lake was lifted Wednesday after water tests showed no presence of toxins from the blue-green algae bloom that has dogged the reservoir since late September.
The water samples collected Jan. 4 came back with no detection of algae-bred toxins, meaning the voluntary advisory closes today after the requisite one-week wait for a possible regeneration of the bloom, said Chad Stuart, the U.S. Army Corps of Engineers' natural resources program manager at the reservoir.
"There wasn't even any algae present in the samples we sent out," Stuart said.
A similar advisory was lifted Tuesday on the South Umpqua River near Myrtle Creek.
That leaves Sru Lake in Coos County and Gerber Reservoir in Klamath County as the remaining Oregon water bodies still under public health advisories.
Blue-green algae is a generic term used for a string of a cyanobacteria known worldwide at times to produce cyanotoxins that are potentially deadly to people and pets.
Lost Creek Lake water sampled in September showed levels of aphanizomenon at more than 25 times the level deemed to be safe for exposure as well as levels of anabaena flos-aquae of more than five times the healthy threshold.
Despite cold weather, the bloom persisted and in turn state and county public health officials retained the voluntary advisory against water contact and eating fish caught from the lake without intense cleaning.
The bloom, however, noticeably ebbed in mid-December, Stuart said.
"It cleared up while a lot of us were on Christmas leave," Stuart said.
Also during the holiday break, the Corps received notice from the laboratory used in its water sampling that holiday vacations among lab workers could mean delays in testing, Stuart said. So Corps officials decided to wait until last week — after the holiday break — to send in their water samples, Stuart said.
"We didn't want the samples to be ruined and have to do it again," he said.
Aphanizomenon and anabaena flos-aquae are both technically bacteria, and along with mycrosystis, form a threesome of so-called blue-green algae that plague Oregon lakes in summers and fall.
The lake, which feeds the Upper Rogue River, had a similar advisory in June that lasted three weeks.
Dangerous toxin levels have never been found at Lost Creek Lake or any other Oregon lake or reservoir. But illnesses and deaths have been documented worldwide, and public health officials nevertheless report its presence and issue advisories as precaution.
There has never been a confirmed human illness in Oregon caused by the algae or its related toxins, though two dogs have died, one in each of the past two years, from algae-related toxins consumed from a large, stagnant puddle along the Umpqua River near Elkton.
Reach reporter Mark Freeman at 541-776-4470 or email at firstname.lastname@example.org.