Hikers and backpackers are warned to steer clear of water contact with a small lake within the Rogue-Umpqua Divide Wilderness Area because of a bloom of a potentially toxic form of blue-green algae.

Hikers and backpackers are warned to steer clear of water contact with a small lake within the Rogue-Umpqua Divide Wilderness Area because of a bloom of a potentially toxic form of blue-green algae.

Fish Lake within the high-elevation wilderness that straddles the Rogue River and Umpqua River watersheds has levels of anabaena flos-aquae that are more than four times higher than state Department of Human Services thresholds for safe.

People who plan to camp at the 90-acre lake were warned against attempting to filter the lake's water because portable filtering systems cannot remove the algae and any related toxins. Also, horses and other animals should not drink from the lake and instead drink from streams or springs in the area, according to the Umpqua National Forest.

Not all blooms create toxic water conditions, which are most common when the algae dies and the toxins are released.

Exposure to toxins can produce symptoms such as numbness, tingling and dizziness that can lead to difficulty breathing. Symptoms of skin irritation, weakness, diarrhea, nausea, cramps and fainting should also receive medical attention if they persist or worsen.

No on in Oregon has proven to be sick from exposure to the algae, which the WHO said has caused illnesses and even deaths elsewhere in the world. A dog died last summer after it consumed algae-laced water along the Umpqua River near Elkton.

The state Department of Human Services has adopted the WHO guidelines, which recommend keeping the advisory in tact for two weeks after the bloom dies to allow for the toxins to dissipate naturally.

However, the advisory can be lifted after one week if tests showed any toxins present are below unhealthy thresholds.

Fish Lake can be reached by two trails hiking west to east in the Umpqua Forest's Tiller Ranger District, forest spokeswoman Cheryl Caplan says. Those are the Fish Lake Trail and the Beaver Swamp Trail.

From the east side hiking west, the Fish Lake Trail can be accessed off Highway 230, but it is a very long hike into the lake and used primarily by packers, Caplan says.

The lake joins Diamond and Lemolo lakes within Umpqua Forest lands that remained under voluntary public-health advisories because of potentially toxic algae blooms.

In Jackson County, Willow Lake has remained under a public-health advisory for an algae bloom since April 21.

— Mark Freeman