To ensure the cleanliness and health of Sunset Lake, the SLA performs water quality testing as part of the UNH Lakes Lay Monitoring Program. Water samples are taken in the spring from the streams flowing into the lake and at various points within the lake throughout the spring, summer, and fall. UNH employees and graduate students visit Sunset Lake once a year in July to do a comprehensive test in conjunction with SLA volunteers.
Water quality has been continually measured in Sunset Lake since 1984 and is reported with four primary values:
In summary, Sunset Lake is best characterized as a relatively clear but moderately nutrient enriched, mesotrophic lake. While the measured quality values have varied slightly over the years, they all have been relatively stable since 1984.
Please see the charts and descriptions below on this page for the trends of each of these values throughout the years. You can also see complete UNH Lakes Lays annual water quality reports for Sunset Lake on our Water Quality Reports page.
E. coli Testing: UNH and the Sunset Lake Association does not perform any E. coli bacteria testing on Sunset Lake. NHDES tests NH freshwater beaches for E. coli bacteria throughout the summer, including at the Hampstead town beach. Visit the Beach Information section of our Sunset Lake Info page for more details about bacteria testing at the Hampstead town beach.
Cyanobacteria: Also known as Blue-Green Algae, cyanobacteria is naturally present in all lakes in rivers, but can take two forms of which the Sunset Lake community should be aware:
For more details about cyanobacteria and benthic mats in Sunset Lake, read this blog post.
As members of the Sunset Lake community, we can all do our part to help prevent degradation and possibly even improve the Sunset Lake water quality. The two nutrients that humans contribute to lakes that can most negatively affect lake water quality are phosphorus and nitrogen. The best way to prevent algae and bacteria growth or too many plants/weeds from growing in the lake is to minimize the amount of phosphorus and nitrogen that flows into the lake. Phosphorus is the main nutrient that plants and bacteria need to grow. By fixing eroding areas and soaking up runoff water on the landscape, limiting the use of fertilizer on lawns, ensuring that septic systems are working properly, and avoiding feeding of ducks and geese the amount of phosphorus and nitrogen in the lake will be minimized.
Visit these pages for more information:
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 from 1985 to 2021.
Tributary (stream) and shoreline water samples help to determine if there is any localized flow of high phosphorous into the lake from septic, fertilizer, construction, or other runoff.
Tributary (stream) samples are taken by SLA volunteers from 21 streams that flow into Sunset Lake soon after ice-out during the spring rainy season when there is good stream flow. The samples are frozen and given to UNH for phosphorous content analysis. If a particular stream is showing a high phosphorous reading in the spring, additional samples may be taken or the shoreline may be monitored more closely where that stream enters the lake.
Shoreline samples are taken from 21 locations near the shoreline when UNH visits in July and analyzed for phosphorous content. SLA volunteers also monitor the lake shoreline regularly for conductivity spikes which can indicate a localized increase in phosphorous concentrations.
Using the map below, you can see the phosphorous test results over the years for the stream sample (T#) and shoreline sample (S#) test locations. Note that the acceptable phosphorous PPB (parts per billion) ranges for streams are higher than those for water samples in the lake since the stream samples are not diluted by the large water volume of the lake.