What is Gleotrichia?

Gloeotrichia (pronounced “glee-oh-tricky-ah”) echinulata is a colonial blue-green algae that forms tiny spheres, which can be seen without magnification in lake water. “Gloeo” has been known to exist in Maine lakes for many years, but it has typically been observed in late summer, in relatively low densities.  However, during the past decade, gloeo appears to have been on the increase in lakes throughout much of New England.  Gloeo blooms have occurred earlier in the summer, and in higher densities than previous decades.


Research on the life cycle of this alga has suggested that gloeo may play a role in declining water quality of otherwise clear, low nutrient lakes. Lake Stewards of Maine (LSM) monitors are working with researchers from Bates College and other institutions that are studying gloeo to assess current trends.  Volunteer lake monitors are now being trained to identify and quantify colonies when they take Secchi disk readings (using a simple density scale developed collaboratively by Maine DEP, LSM and Bates College). The photo shows a highly magnified single gloeo colony. Observed in the water, gloeo colonies appear to be the size of the head of a small pin.

Factors that affect gloeo abundance:

  • Light:  Like many other species, gloeo take biological cues from the intensity and duration of sunlight. They can only grow on sediments that are exposed to light. Lake bathymetry (the shape and contours of the lake bed) will control the area of the lake that is shallow enough for light to reach the bottom (known as the littoral zone). Lake clarity and color also impact how deep light can penetrate. Low clarity and/or high color mean that less of the lake bottom is exposed to light.

  • Temperature:  Cyanobacteria, including gloeo, have higher optimum temperatures than other algae types. Comparison of the population peak and seasonal temperature peak suggest that high temperatures influence the timing of gloeo blooms. Climate change is causing temperatures to rise over time, which could explain why gloeo may be becoming more prevalent in the Northeastern US.

  • Nutrients:  The quality and availability of nutrients within the sediment strongly influences gloeo growth. Most cyanobacteria do not thrive in low-nutrient lakes because they rely on high phosphorus levels within the water. Unlike most algae, gloeo cells divide primarily on lake sediments rather than in the water itself. Sediments contain relatively large amounts of phosphorus, which gloeo uses to grow before floating from the sediment into the water column when they mature. The algae cells can also store excess phosphorus that is used to reproduce once they are buoyant.

In 2016, the Lakes Environmental Association monitored 32 sites on 26 ponds and lakes for cyanobacteria (blue-green algae).  Keoka Lake was sampled 2-5 times.  The table below shows the comparison of peak gloeo concentrations in all lakes tested from 2013 to 2016.  The highest concentration of gloeo was recorded on July 27, 2016 in Keoka Lake.

The gloeo concentrations for Keoka Lake from 2013 to 2016 are shown in the graph below.

From the results of the LEA study, about 60% of the sites sampled had little to no Ggoeo in 2016 and in the previous 3 years of sampling.  Ten sites on 7 lakes have had levels above 1 col/L.  The good news is that most of these sites have stable, relatively low populations as levels. Only Keoka Lake, Long Lake, Moose Pond, and McWain Pond have had gloeo levels above 10 col/L in the four years that LEA has been monitoring the algae.  Levels of gloeo under 10 col/ L are generally considered to be low and not a serious concern.  Because gloeo is large compared to most algae that live in the water column, very low concentrations—even around 1 col/L—can be very visible. This can be an aesthetic concern, but it is not an immediate water quality or human health problem.

Keoka Lake Association, PO Box 97 Waterford, ME  04088