PORT TOWNSEND — Anderson Lake was a popular place Saturday morning when it opened for trout fishing and other recreational uses.

“We had a very full parking lot,” said state Ranger Aaron Terada on Saturday afternoon.

“We had about 85 fishermen on the lake at about 10 a.m.,” he added, pointing out that this is an indication of the number turning out but was not an overall attendance number, which wouldn’t be known until after the park closed for the day.

People were lined up at the gates when they opened at 6:30 a.m., allowing access to the 410-acre Anderson Lake State Park and the 70-acre lake within.

Both will be open from that time to dusk throughout the season.

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 on 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 — the county lakes of Gibbs, Leland and Crocker — said Greg Thomason, Jefferson County environmental health specialist.

Because tests found extremely low levels of toxins, State Parks personnel gave the go-ahead to open the lake for the beginning of the state lowland lake fishing season.

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.

Gibbs is south of Port Townsend. Leland is north of Quilcene.

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.

Fishing already is prohibited at Crocker Lake, which is off U.S. Highway 101 near the intersection with state Highway 104, by the state Fish and Wildlife Department.

“But people do go in there with canoes and small boats, so they expose themselves to algae at the lake,” 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.

The most recent tests were of samples taken last Monday. Results for King County Environmental Labs received late Thursday found no detectable microcystin in any of the lakes sampled.

Anatoxin-a levels — which are measured in micrograms per liter of water — were 0.30 microgram per liter in Anderson Lake, 0.04 in Leland and Crocker lakes, and not detectable in Gibbs Lake, Thomason said.

The safety threshold is 1 microgram per liter.

Sandy Shore Lake looks clear and was not sampled last week, Thomason said.

He warned that though toxin levels are extremely low in the most recent samples, the information lags behind current conditions.

“The last information we have is from the April 23 sample,” Thomason said.

“It can change quickly.

“The toxins are all very low, so it is safe to fish. It is safe to get in the water, but use caution.”

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.

Anyone who observes an algae bloom at a lake is urged to phone the Jefferson County Public Health Department at 360-385-9444.

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

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Managing Editor/News Leah Leach can be reached at 360-417-3531 or at leah.leach@peninsuladailynews.com.