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Water monitoring's 3 key measures

By Dr. Danielle Wain 7 Lakes Science Director


7 Lakes Alliance monitors water quality year-round on each lake in the Belgrade Lakes watershed. When you see us on the water aboard the Colby Compass or our Boston Whaler, or on the ice in the winter, you may ask, “What exactly are they doing out there?”

Our water-monitoring activities involve three key components: measuring water clarity, logging temperature and oxygen profiles, and collecting water samples to quantify phosphorus, chlorophyll and algae.

7 Lakes Science Director Dr. Danielle Wain collects water samples on McGrath Pond last summer. 7 Lakes gathers water-quality samples and data year-round to better understand trends and needed responses.

Clarity is the most obvious indicator of a lake’s water quality. We measure this with a Secchi disk – a black-and-white disk that is lowered into the water until it is no longer visible from the surface. People have been taking these measurements on the Belgrades for over 50 years. So, these measurements help us understand long-term water-quality trends in each lake.


Temperature and oxygen data is gathered by slowly lowering a water-quality probe to a lake’s bottom. Temperature and oxygen profiles tell us if the lake is stratified and whether oxygen is near the bottom. If there is no oxygen at the bottom, sediments can release phosphorus, which can lead to algae growth. So it is important for us to understand how often a lake lacks oxygen at the bottom. The balance between phosphorus coming from lake sediments versus from the watershed (mostly from runoff and erosion) dictates the management strategies we must employ to protect the lakes.


Finally, the water samples we collect finish telling the story. The ways in which phosphorus, chlorophyll (a proxy for algal biomass), and the structure of the algal community change over the course of the year tell us about how a lake’s ecosystem is functioning.


Lakes are not swimming pools. (They would be bad for fishing if they were!) A well-functioning ecosystem provides all sorts of services to the human and ecological communities they serve. When a lake’s ecosystem is out of balance (namely, too much phosphorus), we see nuisance algal blooms and stressed fish populations.


Ultimately, all the monitoring we do helps us tell the story of the lakes each year and why some are “good” years and others “bad.” Each lake is unique, and only by collecting this data can we effectively understand and tell this story.



Colby College student Hans Toulmin gathers temperature and oxygen data using a water-quality probe on Long Pond in February. Water-quality monitoring also involves collecting data for water clarity and phosphorus levels.



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