Friends of Cottage Lake

05/06/2026

Phosphorus treatment - scheduled for Thursday, May 7th, 2026 - no irrigation or recreational restrictions - signs will be placed in yards around the lake May 6th. This is a big treatment, so the motor boat will be out on the lake for most of the day

11/01/2025

Good news - the last two algae samples were below the limit for toxins and the Dept of Health is recommending the warning signs at the park come down.

Here is the full statement from Public Health to King County Parks:
- Toxic algae season is not completely over yet, and algae can come back unexpectedly to bloom again. Please continue to monitor the lake for visible algae blooms.
- The toxin level detected in recent samples is safe enough for humans, but harmful enough for dogs.
- We encourage you to post the signs (see attachment) to encourage the public to stay vigilant even if the advisory is not in place.

Details on the test results here:
https://www.nwtoxicalgae.org/Data.aspx?SiteID=23

10/10/2025

Toxic algae - samples continue to test above safe limits
Monday's sample again came back showing toxin levels above the warning threshold, so warning signs and fences will continue to stay up at the park.

The lake is looking better after the rains, but please continue to be careful, avoid any visible algae, and keep your pets away from the water.

As always, you can find the latest results at

This database contains the most current toxicity data available. All instances of values above the recreational guidelines are kept as up to date as possible, but values below the guidelines may be somewhat delayed in entry.Since there is a lag time from the date of sample to the date of analysis, b...

09/13/2025

Latest algae sample - toxins but below the limit:

"Results from this week’s Cottage Lake algae toxin samples are below guidelines - 6.3 ug/L microcystin and

Send a message to learn more

09/05/2025

Toxic algae warning - the sample from Monday (9/01/25) came back over the limit and warning signs are being posted. From the county:
"We’ve gotten results back from the sample you submitted this week for toxin analysis – 13.5 µg/L microcystin and

07/13/2025

https://www.facebook.com/share/19ELsZuzwW/

Send a message to learn more

06/05/2025

Good news! The toxic algae warning has been lifted.

We received the results back from Monday's sample from Cottage Lake: 0.103 ug/L for anatoxin and 0.6 ug/L for microcystin. With these results we have two samples below State Recreational Guidelines and Public Health has lifted the lake advisory for toxic algae in Cottage Lake.

As a reminder, it is always recommended that you avoid contact with any algae scums and keep your pets from drinking from the lake.

Send a message to learn more

05/29/2025

Lake Treatment on May 30th, 2025

We were able to work with Aquatechnex to squeeze Cottage Lake into their busy schedule on Friday, May 30th. This is the same treatment as last year - no restrictions on irrigation or on recreational use (although the lake is still officially under a warning for toxic algae ( https://www.nwtoxicalgae.org/HealthRisks.aspx ))

Treatments are not cheap (we will limit this year's treatment to $30K due to available funds). We had a couple of large $5K+ donations which allowed us to continue the treatment plan this year but are brainstorming fundraising ideas so we can continue next year. Let us know if you have ideas and thanks to everyone that continues to support Friends of Cottage Lake.

Jonathan Morrison
www.friendsofcottagelake.org

Phosphorus treatment - scheduled for Friday, May 30th - no irrigation or recreational restrictions - here is a presentation from Aquatechnex on phosphorus treatments and toxic algae - Aquatechnex_ Cottage Lake 2024 Results Toxic Algae again detected in Cottage Lake (sample from May 4th): We received...

05/09/2025

We just started up regular lake monitoring again (May 4th) and the first sample submitted was over the limit for Anatoxin-a (one of the two toxins we measure when sampling algae). This is the first time I can remember where we exceeded the guidelines for Anatoxin-a (usually if we close the lake it is due to Microcystin levels).

Public Health is recommending the following: "post WARNING signs at the beach/lake. People and pet animals should stay away from areas where signs are posted and areas of beach/lake where visible algae is present." (so I consider the lake closed to swimming or activities where you will come in contact with the water)

We'll sample weekly until the levels are below guidance two weeks in a row - results are here:

This database contains the most current toxicity data available. All instances of values above the recreational guidelines are kept as up to date as possible, but values below the guidelines may be somewhat delayed in entry.Since there is a lag time from the date of sample to the date of analysis, b...

10/11/2024

Toxic algae was detected again in Cottage Lake (sample from Oct 6th): we received lab results for the toxic algae sample collected on 10/6/2024 in Cottage Lake, and it indicated above-threshold values for microcystins. Please avoid any algae scums you see and consider the lake closed for recreation. Detailed results:

This database contains the most current toxicity data available. All instances of values above the recreational guidelines are kept as up to date as possible, but values below the guidelines may be somewhat delayed in entry.Since there is a lag time from the date of sample to the date of analysis, b...