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 has been relatively stable since 2014 with the exception of wild variations in 2018 and 2019.

 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 four 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 since data has been collected. In most recent years, the color has varied based on wet (darker color) and dry (lighter color) years. In wet years, the water color is darker due to "flushing" of wetlands and stormwater runoff into the lake.