August 2025: 

Chebacco Lake is experiencing a second cyanobacteria event in 2025 with a different species, Microcystis (suspected). Look out for blooms and avoid them! This page will provide regular updates to lake users for the duration of the event. 

What should I do if I suspect a bloom? 

Submit a photo using our Contact Us Form. See Day 5 of Round 1 below for more information. 

After a very low test result on August 21, the results of the August 25 test were unexpectedly high: 95,000 cells/ml and 5 parts per billion of the microcystin toxin. The cell count is above the Massachusetts guideline of 70,000; accordingly, the Essex BOH advisory prohibiting contact with the water there continues. 

As a reminder, the first state test on August 21 came back well below the threshold: just 6,700 cells/ml.

The second criterion level (microcystin toxin) was at 5 ppb, below the state threshold of 8 ppb. The toxin was not found in the August 21 test.

Two points for context:

1. The day of the test (Monday, Aug 25) coincided with an uptick of cyanobacteria sightings around the lake. (Gratitude to our spotters who quickly responded to a request for what they were seeing!) 

2. Hillary Kenyon, our lake consultant, explains that late summer cyanobacteria upticks are not unusual. Cool nights help stir the lake, bringing nutrients up to the surface and stimulating cyanobacteria.

Concern for dogs: Erin Kirchner, the Essex health director, underscores that cyanobacteria at elevated levels can be particularly impactful for dogs who drink the water and lick their fur. 

Labor Day weekend: The health watch continues: Watch for algae blooms and avoid them! Wishing you a wonderful, safe holiday weekend! Best wishes for Sunday's block party (2:00-5:00), open to all on the Wood Drive side of the lake!

Dave Lash

CLWA

Hopeful results from Monday's cyanobacteria test at Centennial Grove: Laboratory analysis showed levels of 6,700 cells/ml, which is well below the Mass Dept of Public Health guideline level of 70,000 cells/ml. The toxin microcystin was not detected in the sample. 

Another promising test next week will enable the lifting of the current advisory that is prohibiting water contact at the Grove. For the rest of the lake, please continue to watch for algae blooms and avoid them! Thankfully, reports of cyanobacteria sightings have fallen off this past week!

In other exciting news:

Huge, huge news from Essex Greenbelt! The words "permanently protect" ring and ring. Given the considerable development battle over the past few years, this is an incredible plus for our watershed! A narrow window to raise $3.7M. Let's all pitch in! (And a grateful shoutout to our many dedicated friends at Save Chebacco!)

The watershed's annual meeting will be full of timely topics:

• Greenbelt's acquisition

• Cyanobacteria prevention going forward

• Initiatives in 2026

• Making CLWA bigger and better

Save the date of Sunday, October 5, from 3-6pm. Join with your Chebacco community!

Details will be forthcoming in the September newsletter.

Dave Lash
CLWA

Conditions since the "high" on August 3rd have largely returned to the pattern of low-density cyanobacteria appearing in random locations for a day or two at a time. 

Responding to two days of cyanobacteria at the very active Centennial Grove swimming area (Aug 10 & 11), the Essex Board of Health issued an advisory to avoid contact with the water. Camp Dory has suspended swimming and boating for the time being. Although little cyanobacteria was observed there yesterday (Aug 14), tests over the next 10 days by state toxicologists will determine when the advisory is lifted.

Please keep your reports coming! Through the generous contributions of many folks, it's possible to assess what's happening lake-wide. CLWA is compiling reports from 16 points around the lake into this chart of cyanobacteria activity. The majority of reports over the past 10 days are green ('Clear' or 'Not Seen'). Low-density reports are noted in yellow.

Algae bloom updates are posted at chebaccolake.org/algae-blooms

If you suspect a bloom, please email with photo to admin@chebaccolake.org

Dave Lash
CLWA

Cyanobacteria is visible along the shoreline of much of the lake and Beck Pond today. Many thanks to the many spotters who have reported and sent photos!

At the Centennial Grove swimming area at noon today, there was blue-green water and swirls (an area about 5x10 feet) at the west end of the beach. Fortunately, there were no swimmers on site.

Cyanobacteria was also visible at the old Hamilton beach (see photo). Also, no swimmers.

The boat ramp had traces of cyanobacteria but no surface swirls.

Open water areas tended to be clear or show very diluted activity.

To repeat though, cyanobacteria was very apparent in many locations around all parts of the lake today. One spotter reported, "There were patches of thicker clumps, like this at the edges of most coves." See photo below.

This is the heaviest day, by far, since the first cyanobacteria sighting back on June 18. Blooms are sometimes triggered by rain washing nutrients into water bodies and stimulating algae growth; the rain Thursday and Friday might be a contributing factor.

Regardless, if you use the water, watch for blooms and avoid them!

We are passing what's been observed to the health directors.

Algae bloom updates are posted at chebaccolake.org/algae-blooms

If you suspect a bloom, please email with photo to admin@chebaccolake.org

Dave Lash
CLWA

Since our Day 1 update on Wednesday, we have received a handful of additional reports, with no increase in the apparent concentration level. One photo from Beck Pond looks to be Microcystis; we're checking on it.

Health Watch signs were posted yesterday at Centennial Grove and the boat ramp to advise the public of the potential health risks. Email, web, and Facebook have been updated as well.  The signs were requested by the Essex and Hamilton health directors in part because these Microcystis sightings are new with an unknown trajectory, and an informed public is the best way to avoid mishap. (On behalf of CLWA, I fully concurred with the signage decision although CLWA is deferring to the public health professionals.)  Watch for blooms and avoid them! Follow the tips noted below. That's been the advice for over a month now. Jointly, the BOHs and CLWA are committed to disseminating cyanobacteria information quickly and broadly. (Our approach parallels that of the National Weather Service in Boston which issued an Air Quality Alert for today so the public could make informed decisions about their activities.) You are the key to collecting useful information. Let us know what you're seeing, even if your area is "all clear" or you're seeing only slight evidence. Please be part of the solution by emailing your observations to admin@chebaccolake.org. Dave LashCLWA

While not conclusive, it would appear that a different cyanobacteria, Microcystis, is present, currently at very low levels. If this identification is correct, Microcystis is another toxin-producing species.

Therefore, as before: watch for blooms and avoid them! As you are aware, there is a health risk to humans and pets.

We have notified the Boards of Health in Essex and Hamilton. 

Details:

Small, low-density outbreaks were spotted in 3 locations along Wood Drive, and near the boat ramp. In addition, a small amount was found at Centennial Grove at the westerly most end of the beach.

This morning, three resident spotters on Wood Drive reported swirls on the water surface, and Russ Camp (board member and biologist) spotted a swirl near the boat ramp. 

Russ and I went to take a look, stopping at Centennial Grove as well.

No swirls were spotted along Lake Shore Avenue at the SW portion of the lake.

Description and photos:

Swirls of tiny particles (bacteria colonies) are visible at the surface and just below the surface. Unlike Dolichospermum, the previous species, no flecks have been reported to date. 

Upon seeing the swirls, a natural question is "Is it pollen?" That appears not to be the case.

Algae bloom updates are posted at chebaccolake.org/algae-blooms

If you suspect a bloom, please email with photo to admin@chebaccolake.org

Since the last update on June 28, flecks have reappeared in various places (thanks for your reports!!), but we have not received any new reports indicating concentrated blooms (blue-green water, scum, surface coating, or floating mats). In a Facebook post yesterday, Erin Kirchner, Essex BOH Administrator, summed up where things are at:

Chebacco Lake at Centennial Grove is open! [That said,] we have had reports of cyanobacteria at the lake this summer, and while we're not "closing" it to recreational use just yet, we do ask people to be aware of what a cyanobacteria bloom looks like and avoid it (this includes swimming and also letting your pets swim/drink the water when a bloom is present).

Here's more: 1. Fleck history: June 23 (Day 6): flecks seen in open water across much of the lake. June 28 (Day 11): lake consultant Hillary Kenyon surveyed a good part of the lake, finding no visible cyanobacteria activity. June 30 through today (Day 13-16) flecks reported in small, local pockets. 2. Fleck photo: Here's a typical photo:

3. Meeting with BOH directors: Erin Kirchner, Peter Mirandi (Hamilton BOH), Hillary Kenyon, and I met on Tuesday morning to review the latest information and reaffirm the "Watch for Blooms - Avoid Them" message. Jointly, we have posted an informational flyer at the boat ramp and Chebacco Woods:

4. Should we swim on the Fourth? We have no confirmed report of a harmful algae bloom meeting the Massachusetts threshold, but a toxin-producing cyanobacteria is present. Ultimately, water contact is an individual decision. The public statements by the BOHs can be found at Essex and Hamilton. Erin (Essex) has posted the following tips to minimize the risk of illness from a harmful algae bloom:

• Do not swallow water. Ingestion is a primary concern since ingesting small amounts of cyanobacteria or cyanotoxin can cause gastrointestinal symptoms while larger amounts may cause liver or neurological damage.

• Rinse off after any contact with the water. Contact with cyanobacteria can cause skin or eye irritation.

• Keep animals away. HABs are toxic to pets.

5. Algae bloom updates are posted at chebaccolake.org/algae-blooms

ADDITIONAL INFO ON CYANOBACTERIA

5. Where are the flecks coming from? From Hillary: What you see on the "first days" of a "bloom" is weeks+ in the making in other locations on the lake [bottom] sediment or [in] the water column. Cyanobacteria cells are constantly moving, dying, replicating, and changing in colony size and position within the water column.

6. Flecks are a flashing yellow light. Once they rise to the surface, they might mass into a concentrated bloom (with possible health implications if a toxin-producing species) or dissipate. Wind, sun, and nutrient levels in the surface water all play a role; accordingly, the trajectory is unpredictable, but flecks alert us to a potential problem!

7. To recap: we do not know of a concentrated bloom that has reached the cell count of 70,000 cells/mL. In total, only three blooms have been reported. Hillary has tested at Centennial Grove and the south end of the lake (3 tests total), finding cell counts below the Massachusetts criteria while identifying the cyanobacteria currently present as Dolichospermum, a toxin-producing variety. Visual identification to date suggests we are at low levels of the cyanobacteria.

8. To learn more about cyanobacteria, invest 10 minutes reading/viewing a helpful webpage by a Wisconsin group, the Clean Lakes Alliance. The FAQs build to "How Can I Enjoy the Lakes and Stay Safe from Cyanobacteria?"

Wishing you all a happy Fourth of July!

Dave Lash
CLWA

PS. Algae bloom updates can be found at: https://chebaccolake.org/algae-blooms/

It' s the weekend and, happily, this update can be brief:

1. Good news! Yesterday, lake consultant, Hillary Kenyon, surveyed a good part of the lake finding no visible cyanobacteria activity. The blooms that raised the concern on Day 1 (June 18) and the widespread cyanobacteria flecks across much of the lake on Day 6 (June 23) are generally no longer visible.

2. No new blooms have been reported over the past 10 days. 

3. This has been an inspiring community effort. The health directors in Hamilton and Essex, Peter Mirandi and Erin Kirchner, have been incredibly responsive. Lake residents and users have been sharing what they observe and volunteers have signed up to do ongoing bloom monitoring. Thanks to one and all!

4. This won't be our last cyanobacteria algae bloom. The first steps are being taken to establish a threat index, combined with monitoring and communication for all lake users, including those using the boat ramp and Centennial Grove who are not on our email list. To play a part, email admin@chebaccolake.org

5. The timing of Hillary's coincidental trips to the lake were fortuitous, adding a true expert guide to the work we've done together. She's here because Essex, Hamilton, the Commonwealth, and the CLWA ponied up over $50,000 in FY2025 to begin the meaningful work of developing an actionable lake and watershed restoration plan which will, in part, help prevent harmful algae blooms (HABs) in the future.

6. Harmful algae blooms, "weeds and muck," diminished water quality, and recreational impairment all stem from excessive nutrients and "dead zones" of depleted dissolved oxygen. If you haven't already, read our Godzilla Algae is Coming! article.

7. Watch for the CLWA newsletter arriving early next week.

8. Keep a lookout for algae blooms and avoid them!!

9. Wishing you a wonderful, lake-filled weekend and Fourth of July!

Dave Lash

CLWA

PS. Algae bloom updates can be found at: https://chebaccolake.org/algae-blooms/

The toxin-producing cyanobacteria, Dolichospermum, commonly emerges in early summer and often tapers off. Some studies suggest it peaks between May and June.

Yesterday, Hillary analyzed a sample from the Grove swimming area, finding that the cell count was below the state threshold, but higher than the initial sample from the south end. Hopefully, readings will stay low.

No new bloom reports came to CLWA today. Hillary checked Beck Pond yesterday and it seems to be clear.

Flecks of cyanobacteria in open water yesterday have moved in many cases. For example, flecks at the Grove's swimming area that Erin Kirchner spotted yesterday morning were not present when she returned this morning. On the other hand, flecks appeared in new locations including parts of Echo Cove.

One likely scenario is that concentrated blooms (those presenting the most health risk) will move, or rather appear and disappear. Hence the emphasis on visual identification and vigilance by lake users!

Are flecks indicative of a bloom? Hillary says 'yes' in that an emergence is occurring. On the other hand, a DPH staffer says 'no,' given that toxin concentration is typically quite low. Whether they're called a bloom or not, flecks are a useful indicator of cyanobacteria activity warranting caution. We're lucky to have them actually!

The biggest news of the day is that health directors, town managers, and I met this morning to discuss how we can best work together. We are joining forces on communications, public awareness (including posting), and testing with the hope of navigating through this event safely and with the least disruption. We'll meet again next Tuesday, hopefully after additional test results become available.

Updates can now be found at: https://chebaccolake.org/algae-blooms/ 

Dave Lash

CLWA

A toxin-producing cyanobacteria, Dolichospermum, has been identified by CLWA's lake consultant, Hillary Kenyon, from a sample taken from the algae bloom at the south end of the lake.  To date, the levels are very low -- below the levels that Massachusetts uses to determine potential threats to the health of humans and pets -- however, the blooms could worsen. Be on the lookout for blooms and avoid them! (And protect your pets.)  Three small algae blooms have been reported (see June 22 email); no new blooms were reported today. New: Cyanobacteria flecks (see photo below) can now be seen in open water across much of the lake. They are considered too diffused to be harmful in open water; the health risk is when they accumulate in blooms near the shore. The Essex Board of Health has posted an alert on their website and Facebook page. Read their tips. CLWA and the Essex BOH each notified the YMCA who suspended swimming activities at Camp Dory located at Centennial Grove. Hillary took a sample from the swimming area for testing.  We are meeting with the Essex and Hamilton BOHs tomorrow morning to discuss further measures. Posting at the boat ramp is a priority. CLWA is creating a webpage to record updates. It will be operational by Tuesday, June 24. Go to our Watershed Stewardship page and click on the Algae Bloom section.  We'll continue to email updates periodically as new information comes available. To receive email updates, subscribe to our newsletter; we're using that list for bloom updates.

ALERT FROM CLWA

Small pockets of blue-green algae have been reported near the boat ramp, at Red Gate Road, and Echo Cove. No other sightings have been reported to date. The trajectory of the growth and the potential risk to humans and pets is not currently known.

The lake association is contacting the Boards of Health and we will update you regularly as we learn more. Please be on the lookout for possible blooms and report them to CLWA with location and photo (if possible). 

At this early stage, without knowing if the blooms are a toxic form of cyanobacteria, contact with the water is a personal decision. Read about the potential health risks to humans and pets, and make your own decisions. The CLWA is not qualified to give public health advice, but we hope these FAQs will be helpful:

What do we know about the blooms reported to date?

The first report was from our lake consultant, Hillary Kenyon. The bloom was near the boat ramp and was small, near the shore, and identified visually (not by testing) as cyanobacteria.

The second sighting was on Red Gate. The blue-green water in the photo is suggestive of cyanobacteria.

The third sighting is at the southern end of Echo Cove. 

Three property owners have reported the absence of a bloom at the north end of Echo Cove, in Gregory Island cove, and along Lake Shore Avenue.

What happens next?

We are reaching out to the Boards of Health in Hamilton and Essex, and the Towns, to coordinate a plan for identification and public awareness. In speaking with Hillary, she indicated that effective bloom monitoring and response is typically a collaboration of the lake association, the BOHs, and towns -- no single organization is responsible for algae blooms lake-wide. (The Essex BOH is responsible for monitoring and management of the swimming area at Centennial Grove.)

If I don't see a bloom, how much risk is there to go in the water?

(Thank you, Bill Haugh, for the question.)

This is the question that many of us are asking. Sorry, but here's our non-answer! Massachusetts rates the health risk as a function of concentration:

DPH recommends issuing a public health advisory for HABs at recreational freshwater locations when at least one of the following criteria is met:

1. A visible cyanobacteria scum or mat is evident;

2. Total cell count of cyanobacteria exceeds 70,000 cells/mL;

3. Concentration of the toxin microcystins exceeds 8 µg/L; or

4. Concentration of the toxin cylindrospermopsin exceeds 15 µg/L

Guideline values are based on US Environmental Protection Agency (US EPA)1 and World Health Organization (WHO)2,3 recommendations. 

The Guidance for Vermont Communities (pages 11-12) offers three levels of suggested action based on a visual monitoring system. Category 2 (when cyanobacteria is present in low to moderate amounts) says, "May be appropriate to alert water users to be on the lookout for possible blooms and to avoid them."

Reviewing the numerous advisories in NH last summer, it was noteworthy that most advisories were for small portions of water bodies where blooms were identified visually or by testing. 

Perhaps the BOH will have other information to provide. Again, CLWA is not qualified to offer advice on health risks.

How do we get rid of a harmful algae bloom?

As we have been emphasizing since the 2020 outbreak, good lake and watershed management can dramatically reduce the occurrence of harmful algae blooms (HABs), but once a bloom appears, we can only wait it out and ensure public safety until the bloom naturally dissipates. (Thanks to all of you who are supporting our watershed study and planning through your membership and donations!) 

Are there simple, no-cost tests for blue-green algae?

Yes, and we all need to become proficient in visual identification. Is it pollen or algae, for example; and is a filamentous string of algae hazardous? 

Most of the algae growing in lakes and ponds is non-toxic, so learning to eliminate non-toxic "stuff" is the first step. The stick test and the jar test are easy to do. Here are two simple places to start: 

Stick and jar tests

YouTube (7m) How to Identify Harmful Algae Blooms

What should I do if I suspect a bloom? 

For right now, email details with a photo to admin@chebaccolake.org. If more locations are identified, we will post sightings to a Google Doc and share the link.

Dave Lash

CLWA

CLWA tapped our lake consultant, Hillary Kenyon, of Applied Watershed Sciences, for guidance on cyanobacteria blooms, how to monitor, and how to communicate with the community. Key takeaways:

• In many ways, visual identification in Hillary's view is more important than quantitative sample testing which is time-consuming, slow, and rarely representative of the entire water body. 

• Teach everyone how to identify blue-green algae blooms and to avoid them.

• It is possible but unlikely that there will be a uniform high-density bloom across the bulk of the lake; instead, it's more likely that there will be shoreline blooms here and there.

• Cell counts are likely to vary widely; Hillary has seen situations where cell counts are in the millions on one side of a lake and barely reading on the other. Therefore, use quantitative testing selectively.

• Accordingly, for a lake of our size, it's vital that individual blooms be identified quickly (by visual identification) and avoided rather than closing the whole lake (unless densities spike everywhere).  

• Most importantly, effective bloom monitoring and response, including public awareness, requires  meaningful collaboration between a lake association, BOHs, and Towns.

Acting on Hillary's advice, CLWA began working to notify and educate the community, and reach out to the BOHs and town managers in Essex and Hamilton.

Lake consultant Hillary Kenyon observes a small, shoreline bloom at the south end of the lake which she visually identifies as a likely cyanobacteria.

A second bloom at Red Gate Rd is reported with a photo suggestive of cyanobacteria.