PORT TOWNSEND — Anderson Lake will be open for fishing and other recreational use Saturday.

The popular trout-fishing lake, and the entire 410-acre Anderson Lake State Park surrounding it, will be opened for the season that day, said ranger Aaron Terada on Friday.

“It is going to be open,” he said. “We’re opening tomorrow.”

Gates open at 6:30 a.m. and the park remains open until dusk.

A Discover Pass is needed to visit the park. It can be bought at the state park, and costs $10 for one-day use or $30 for an annual pass good for one year from the date of purchase.

Although the date of the opening of the entire park was never in doubt, the lake’s status depended upon the results of tests for algae-produced toxins in the water.

Two toxins historically found in some East Jefferson County lakes are anatoxin-a, a quick-acting nerve poison that can cause convulsions and stop breathing, and microcystin, which can cause skin irritation and, if ingested over a period of many years, can result in liver failure.

The most recent tests found that the levels of these two toxins were way below safety thresholds, not only in Anderson Lake but also in the other lakes sampled — Gibbs, Leland and Crocker — said Greg Thomason, Jefferson County environmental health specialist.

But since species of algae known to produce toxins are present — even though they apparently are not active now — caution signs have been placed at Anderson, Gibbs and Leland lakes.

A caution sign also has been erected at Crocker Lake, but for a different reason: unlike the others lakes, it has a visible bloom of algae.

It is not yet known if the Crocker Lake algae is of the type that is known to produce toxins, Thomason said.

The county’s yellow caution sign warns lake users to refrain from drinking lake water and from swimming or boating in areas of scum.

It also urges users to keep pets and livestock away from it and clean fish well and discard guts.

Blue-green algae flourishes in warm temperatures when sufficient nutrients, such as phosphates, are present.

But researchers don’t understand why some species of blue-green algae begin to produce toxins, nor what makes them increase.

Since 2006, the 70-acre lake in Anderson Lake State Park has been closed during parts of the warmer months because of dangerous levels of toxins.

No toxic blue-green algae has been reported in Clallam County, where health officers do not test for toxins. Instead, they visually monitor lakes for signs of algae bloom.

Algae blooms in Clallam County lakes should be reported to the Clallam County Department of Health and Human Services’ environmental health division by phoning 360-417-2258.

Blooms in Jefferson County can be reported at 360-385-9444.

For more information about lake quality in Jefferson County, visit the environmental health website, http://tinyurl.com/6z64ofy.