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Photo courtesy of Don Yurewicz

Conway Lake Water Quality

If you swim, ski, kayak, fish, or boat on Conway Lake you understand how fortunate we are to enjoy such a pristine body of water. Monitoring water quality has been one of the chief concerns of the Conway Lake Conservation Association (CLCA) since its inception and is one of the ways we track the health and further our understanding of the lake’s ecosystem. The CLCA water quality testing program includes two components:

1.  Lake Samples: In depth measurements are collected by Mike Wolf at five deep lake sites  weekly over the course of the summer.  Test results are compiled by Bob Craycraft at UNH and the report for Conway Lake can be found on-line at the UNH site:

2.  Stream Samples: Stream samples are collected in the spring and fall by Maria Gross, Bill Petry, John Edgerton and Don Yurewicz from 14 tributaries that feed into Conway Lake.  These samples allow us to monitor contributions from individual drainage areas within the greater Conway Lake Watershed.


After a brief work up of these samples they are then forwarded to Bob Craycraft, Director of the UNH Lake Monitoring Program.  Not only do they do further lab analysis, but they also keep an official recording of the annual results for the past thirty-seven years.  After assessing the most recent data they conclude that Conway Lake continues to retain its “oligotrophic” status as a pristine body of water.  We must all work together to help maintain Conway Lake as a pristine body of water for future generations to enjoy!  Learn more about what you can do as a homeowner on Conway Lake at:

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Measuring water clarity.  A black and white 'Secchi' disk is observed from a boat as it is gradually lowered into the lake. The depth at which it is no longer visible is the “Secchi depth” and is a measure of the clarity of the water column.
Collecting a stream sample to measure nutrients entering the lake from one of the lakes watershed tributaries.  Stream flow is also measured to determine the relative contribution of different tributaries.

Testing Results

Water measurements conducted on lake samples include water clarity (transparency), dissolved oxygen, phosphorous, chlorophyll-A, and water color.  Below is a brief summary of each.

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Key measurements for the past 4 years of published data.  These measurements are season averages for approximately 20 testing dates at 5 locations around the Lake.  Green shaded boxes represent data indicative of oligotrophic conditions whereas the orange shaded numbers are indicative of mesotrophic conditions.

Water Clarity is an important measure of a lake’s health.  It affects the depth to which aquatic plants can grow, dissolved oxygen content, and water temperature. Fish, loons and other wildlife depend on good water clarity to find food. Primary factors that influence water clarity are suspended sediments from runoff and, algal growth, and acids transported into the lake from adjacent wetlands.  Water clarity depths can be highly variable from year to year depending on rainfall or snowpack melt that carry suspended sediments into the lake.   Water clarity in 2019, for example, was lower in Conway Lake from previous years, largely due to the very wet spring we experienced and increased runoff.  This result was consistent with other lakes in the area and the clarity improved as the summer progressed.   Data collected over a thirty-seven-year span is shows an overall stable depth averaging just over 18 ft. 


Phosphorous: Phosphorus is usually considered the “limiting nutrient” in aquatic ecosystems, meaning that the available quantity of this nutrient controls the growth rate of algae and aquatic plants. In excess quantities, phosphorus can lead to  excessive algal and cyanobacteria growth (blooms) which may contain dangerous levels of toxins. Since phosphorus generally occurs in small quantities in the natural environment, even small increases can negatively affect water quality and biological conditions. At the current levels found in Conway Lake, phosphorous is in balance and does not cause problems. Excessive phosphorus is often caused by human activity including use of lawn fertilizer and failed septic systems that can leach into the lake. These can be accelerated by storm runoff, both from lakefront properties and from sources elsewhere within the watershed. The overall concentration has shown a decreasing trend over the life of the testing program as shown in the chart below.

Dissolved Oxygen: Dissolved oxygen is a measure of the health of the Lake and its ability to support aquatic life.  It is especially important  for cold water fish such as salmon and trout which require higher levels. Dissolved oxygen levels vary with depth as controlled by lake stratification and range from just over 8 mg/l near the surface to about 2 mg/l in the deepest portions of the lake.  This factor has remained in the average range for the last four years.  

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GIS mapping by Don Yurewicz

Conway Lake Watershed showing tributary streams and water sample locations.  The Conway Lake watershed encompasses 12,820 acres with more the 14 tributary streams.  The largest contributor to the lake is Snow Brook which enters the lake in South Cove. Snow Brook and its tributaries constitute nearly half of the total watershed. There are full-size maps of the watershed under the Resources /Maps tab.

Chlorophyll-a: Chlorophyll-a is the most common photosynthetic pigment found in plants, algae, and cyanobacteria and is used as a means to measure their productivity in a waterbody. Although algae and cyanobacteria are a natural part of freshwater ecosystems, too much algae can cause aesthetic problems such as green scums and bad odors, and can result in decreased levels of dissolved oxygen. Some cyanobacteria also produce toxins that can be a public health concern when they are found in high concentrations.  2019 showed a slight decrease but the longer trend  is one of increasing concentrations.


Color: The Conway Lake color is the result of naturally occurring “tea” color substances from the breakdown of soils and plant materials. The data for the lake display a trend of increasing concentrations over a thirty-five year span (see the chart above).


Volunteers collect weekly water samples from the lake during the summer months and test them for clarity and content. Volunteers use their own boats for this. To volunteer contact Kin Earle: (978) 884-8541


Water samples are also taken from tributaries semi-annually. To assist with collection of stream samples contact Maria Gross (603-491-3107) or Bill Petry (781-929-2021).

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Dissolved oxygen profile at Gull sampling site (just east of Ship Island). Click figure to enlarge.
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