2026 Weekly Cyanobacteria Emails to Monitors

According to reports, cyanobacteria blooms across monitoring sites varied in intensity this week. On Lake Champlain, 17% of reports indicated low or high alert blooms, with many of the blooms located in St. Albans Bay, the Inland Sea, Main Lake South and Main Lake North. Of the 28 reports from Vermont Inland waterbodies, 11% indicated high alert blooms. This week's header photo features jar samples collected from Lake Champlain monitoring sites. 
 

Cyanobacteria appeared in many forms this week, from subtle green concentrations along the shoreline to dense surface accumulations. Of the 120 observations submitted for Lake Champlain, 29 documented bloom conditions, with much of the activity concentrated in St. Albans Bay, the Inland Sea, and Missisquoi Bay. Across Vermont’s inland waterbodies, monitors submitted 33 reports from 12 waterbodies, with one low alert and six high alerts, including the bloom at Shelburne Pond.

This week marked the highest bloom activity of the 2026 monitoring season so far. Of the 164 reports submitted, 60 (36%) documented bloom conditions, including 17 low alerts and 43 high alerts. St. Albans Bay and the Inland Sea experienced particularly high bloom activity relative to the number of reports received. This week’s header photo captures one of the high alert blooms reported at St. Albans Bay Park.

Pink-purple blooms of Planktothrix continued at Silver Lake this week. This type of cyanobacteria looks quite different from the green blooms more commonly reported in Vermont, forming long, stringy strands that have been described as looking like pink or purple “silly string.” VTDEC volunteers have been diligently monitoring Silver Lake throughout the summer, helping us better understand when and where these unusual blooms occur.

Bloom activity was high this week, with 24% of reports indicating bloom conditions, including 31 high alerts. These photos capture blooms from around Lake Champlain and Lake Carmi, many showing a familiar combination of calm water and dense green surface scums.

Bright green surface scums were a common sight among this week’s bloom reports. This Category 3 (high alert) bloom off Stanley Drive in Philipsburg, QC, is a great example of how calm water can allow cyanobacteria to rise and gather at the surface, forming a vivid green accumulation.

Bloom activity remained concentrated in St. Albans Bay this week, where 67% of reports documented blooms. The Category 3 (high alert) bloom at Hathaway Point pictured shows just how dense conditions became, with a thick shoreline accumulation and a jar sample packed with cyanobacteria.

This week, St. Albans Bay recorded one of the highest percentages of cyanobacteria bloom reports on Lake Champlain this season. These images from Hathaway Point Boat Launch show a Category 3 bloom, including the shoreline accumulation, a jar sample confirming the dense layer of cyanobacteria colonies, and a microscope view.

Lake Champlain continued to see relatively few cyanobacteria blooms this week, with just three high alerts and six low alerts reported across the lake. Pictured is one of this week's Category 3 blooms at Black Bridge in St. Albans, VT, one of only two lake regions to report high alert conditions.

After several active weeks, bloom reports declined across Lake Champlain, with 12 blooms documented and no blooms reported on Vermont's inland lakes. Although wildfire smoke created hazy conditions throughout the week, monitors continued to submit reports. The Category 3 bloom pictured above at Cedar Lane in Willsboro, NY, formed green thick streaks along the shoreline.

Volunteers submitted 201 monitoring reports this week, with nearly one in four reports documenting bloom conditions on Lake Champlain. St. Albans Bay experienced the highest percentage of blooms, while Main Lake Central received the greatest number of monitoring reports. The Category 3 bloom pictured at Button Bay Boat Launch in Ferrisburgh, VT, formed a dense green surface accumulation stretching across the nearshore waters.

Week 3 brought cyanobacteria blooms to several regions of Lake Champlain, with 14% of monitoring reports indicating bloom conditions. Missisquoi Bay recorded the highest percentage of blooms relative to the number of reports received, with one-third of montioring reports documenting bloom conditions. 

The second week of monitoring brought the season's first widespread reports of cyanobacteria blooms, with monitors documenting green surface accumulations and shoreline scums at several locations around Lake Champlain and inland lakes. The Category 3 bloom pictured above, reported from Philipsburg, Québec, formed a dense, spilled-paint-like scum that extended along the shoreline.

The first week of monitoring kicked off with rainy weather and a range of generally safe conditions around Lake Champlain - though some phenomena including turbid waters, pollen-filled shorelines, and rocky habitats coated with filamentous green algae provided a good early test in identifying circumstances that are not cyanobacteria. Thank you to our volunteer monitors for a great first week of tracking water quality across the basin.