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'Algae' bloom threatens to close Lake Oswego Swim Park

Lake Corp officials will treat the growth, but say tests show it's not toxic

SUBMITTED PHOTO - The Lake Oswego Swim Park is free and open to all residents of Lake Oswego. Its usually open from July 1 through the end of August.An algae bloom threatened to close the Lake Oswego Swim Park on Thursday morning, but water quality experts said tests showed the water was safe and the park opened as usual in the afternoon.

Jeff Ward, lake manager for the Lake Corp, told The Review that the algae growth is not toxic, but he did say it is highly irregular — especially for this time of year.

Ward said a southwesterly wind drove the bloom to the area around the outside of the swim park on Oswego Lake, creating a greater concentration than normal.

Technically speaking, the blue-green algae — scientifically known as lyngbya — is not algae but rather a species of phytoplankton, one that is particularly buoyant and more often seen on the surface of the water.

“If you have a thick scum on the surface, it can give you a stomach ache,” Ward said. “It’s not for human consumption.” But a water quality scientist for the Lake Corp looked at the growth, Ward said, and determined that it was not toxic.

To treat the bloom, Lake Corp will be applying small doses of aluminum sulfate, known as “alum,” a common antidote used in lakes throughout the country. Alum binds itself to the phosphorus in the blue-green algae, essentially starving it of its nutrients.

Ward said he expects to see the growth come under better control by the end of next week.

“You’re always going to have algae growing in water, and right now, we’re at a sweet spot: the perfect temperature, it’s getting just enough nutrients and sunshine. So it’s going to take off,” Ward says. “What we try to do is control the nutrients in the lake so it can’t go crazy.”

Ward said the unseasonably warm weather is largely to blame for the bloom.

“One of the things that makes this year different is that a lot of times we’ll get 90-degree days, but at end of July, or August, or into early September,” he said. “(This year), we got them at the time of year when the days are longest. We almost never see that in Oregon. So what happens is, not only that the water warms up, but you have so much more sunlight, and optimal conditions, for this algae to thrive. That’s part of what the particular challenge is this year.”

The Lake Oswego Swim Park is located at 250 Ridgeway Road. It’s open from 1-6 p.m. daily, from July 1 through the end of August. For more information, call 503-953-9325 during normal operating hours.

Contact Saundra Sorenson at 503-636-1281 ext. 107 or ssorenson@lakeoswegoreview.com.