Why Picocyanobacteria (Pcy) and Why Now in Highland Lake?

posted Oct 4, 2017, 4:20 PM by Joseph Bickard   [ updated Oct 4, 2017, 4:20 PM ]


Potential Contributing Factor









Land Development




Other urban lakes in Maine are not experiencing a bloom.

Nutrient Loading (P &N)




Although there has been no consistent trend of average annual P concentrations, more intensive study is required leading up to and during the Pcy bloom to determine whether there is a correlation between nutrient levels (P&N) and Pcy growth during that short period.  Since Pcy’s are present in most water bodies, the mere presence of Pcy’s is not because of Highland Lake’s higher nutrient levels.

Chemistry (Ca & Mg)




“Hardwater” lakes favor some types of zooplankton while “softwater” lakes favor others.  Also influences solubility of  nutrients. Very limited data available.

Acid Rain




Acid rain can lead to “softening” of lake water (see above).

Dissolved Oxygen




Lake has experienced low DO in Hypolimnion since 1990s.  Pcy bloom is relatively recent occurrence.

Water Temperature




Bloom occurs during warmest portion of summer.

Weather (Air Temp & Precipitation)




Bloom has occurred both in dryer/warmer years and wetter/cooler years.

Zooplankton Depletion




Zooplankton population collapses during bloom.

Alewife Return




Predation by alewives likely contributes to collapse of zooplankton population. *Alewife return numbers and associated predation of zooplankton are variable from year to year.





Rental and camp septic systems at maximum usage during bloom period but limited data shows no notable increase in N loading to lake during that period.

Boat Traffic




Traffic has not significantly increased over last 4 years.





Firework usage has increased but they now have lower P content. No notable P increase after July 4.


“Invasive” Wildlife




Eagles have returned but they would have only helped in reducing alewife population.

Fish Stocking




Stocked game fish have likely been replaced by native bass population since the cessation of the stocking program, thus no change in overall alewife predation.


Note: The above table reflects the general level understanding, as of September 26, 2017, of the picocyanobacteria bloom in Highland Lake that has occurred during a three to four week period over the past four summers.  Since phosphorus is considered to be the limiting nutrient for algae growth in freshwater systems, and the phosphorus levels are generally above the healthy lake target of 10 ppb that was established in the 2003 Phosphorus Control Action Plan, current phosphorus levels are a major concern in light of both the picocyanobacteria and metaphyton blooms that currently occur in the lake.  Sources of information used to create the table include data collected by the Highland Lake Association Water Quality Committee, Maine Department of Environmental Protection (MEDEP), Portland Water District, various academic institutions, experts associated with the various academic institutions, technical peer reviewed papers, individuals within the MEDEP, and various online sources.