Water Quality Testing

The overall health of the lake over the years is judged primarily by water clarity, microscopic plant life, phosphorus, and water color. The charts below summarize water samples taken at a site in the center of the lake and are the median values of samples taken when UNH visits in July along with additional samples taken by SLA volunteers at other times throughout the year.

Secchi Disk Transparency is a water clarity measurement and has displayed a slight trend of decreasing water clarity since 1984. On a positive note, the Secchi Disk transparency was relatively stable between 2014 and 2017 before varying widely the past three years.  

 Chlorophyll ɑ concentrations, a measure of microscopic plant life within the lake, display a trend of increasing concentrations since 1984. On a positive note, the chlorophyll ɑ concentrations have stabilized since 2010  with lower seasonal average values documented over the past three seasons. From this graph and the previous Secchi Disk Transparency graph, you can see the relationship between plant growth and water clarity; when plant growth goes up, water clarity goes down (2007 and 2009 are good examples). 

 Phosphorus is the nutrient most responsible for microscopic plant growth. The total phosphorus concentrations have oscillated over the years while the long‐term trend suggest a slight reduction (improvement) in total phosphorus concentrations  Phosphorus data is often correlated with the amount of plant growth; increased phosphorous contributes to increased plant growth. 

Lake water color is a result of naturally occurring “tea” color substances from the breakdown of soils and plant materials. Color has varied annually and displays a relatively stable trend from 1985 to 2020.