sunrise.jpg

Conway Lake Sunrise - photo courtesy of Mark Guerringue

Boat Ramp to be Repaired

Repair of the boat ramp on Mill Street has been delayed to 2023.  

Phosphorous Update Fall 2021.jpg

Tributary Phosphorous 

Fall 2021 Update

This past Fall, Bill Petry, Maria Gross, and Don Yurewicz systematically collected water samples from 15 streams that feed into Conway Lake.  The table to the left shows the phosphorous levels of the streams we sampled.  The samples were analyzed on an expedited basis by Bob Craycraft's lab at UNH.  We had requested the analysis be conducted as soon as possible as we were concerned with the increases in the Fall 2020 results.  Bob was very responsive to our request and provided his assessment of the results which were reassuring.  Bob stated that the absolute levels were consistent with other healthy lakes in the area.

 

As can be seen in the table the average amount of phosphorous in all 14 streams decreased 15% from Fall 2020 to Fall 2021 collections.  This variation has many elements, and recent precipitation is suspected to be a driver.  We attempt to collect our samples soon after a rain event, but warm or wet seasons have an uncontrollable major impact. 

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, however, 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. 

 

We must all remember that what happens on our property affects the lake - to this end please prevent runoff into the lake,  curtail the use of fertilizers, and be sure your septic system is operating correctly.

Remapping Conway Lake Bathymetry (Water Depth)

A project was initiated in July 2021 to remap water depth across Conway Lake.  The current map available from the NH DES greatly oversimplifies lake floor topography and overextends the area of shallow water.  This impacts the areas that need to be patrolled for aquatic invasive plants in the lake.  A portable sonar device that records water depth and latitude/longitude and a sounding line were used to collect raw data.  Over the course of last summer, 70 transects were made across the lake that collected over 100K sonar data points.  The data were then downloaded into GIS mapping software to create a new depth map.  Large rocks and boulders were also mapped based on Google satellite images of the lake.  Additional data will be collected in 2022, but in the meantime, an interim map is available on the CLCA website – see the Maps folder on the Resources webpage.

So, what does the new map show?  For one it depicts a much more accurate limit to the shallow water littoral zone (depths less than 15') where aquatic plants can grow and where the AIS patrol needs to patrol for possible invasive plants.   The mapped area of aquatic plant growth has decreased by roughly 50%.  Reducing the area of shallow water has in turn increased the total volume of the lake by approximately 30%.

Sonar profiles and depth data show that the axis of the lake is characterized by a gently sloping and smooth bottom – probably the result of glacial scouring, whereas the margins of the lake are marked by numerous submerged knolls, some of which break the surface, or are shallow enough to be boating hazards.   Most of these were not shown on the old map.  These knolls are probably erosional bedrock highs capped with glacial till left by retreating glaciers.  Lake margins vary from gentle slopes (e.g., the north end of the lake), to steep cliff-like escarpments, to terraced step-down margins.  The deepest measured point in the lake is still 49’ and sits directly east of Andrews Point.  There is a spot nearly as deep (48’) ENE of Ship Island. 

Click here for a more detailed description of the project and summary of findings.  For questions about this project please contact Don Yurewicz (don.yurewicz@gmail.com).

sonar transects.jpg
Map of sonar transects across the lake.  Red dots are depth readings from a sounding line.
Bathymetry map update.png
Depth Legend.jpg
Depth Legend.jpg