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Conway Lake Sunrise - photo courtesy of Mark Guerringue

What's New on the Lake

Winter Life Below the Ice (If there was any...)


Feb 1, 2023 Updated Feb 9, 2023

Reprinted with permission of the author.


Past algal bloom below the ice on Lake Winnipesaukee. (Courtesy photo)

Have you ever stood out on a frozen lake, looked out across the icy bay and wondered what was happening beneath your feet? As we wait for Lake Winnipesaukee to freeze over, let’s explore what will happen to the lake’s ecosystem under the ice.

Last fall, the Lake Winnipesaukee Association published an article in the Laconia Daily Sun discussing the phenomenon known as lake turnover, which in Winni occurs once in the fall and once in the spring. To briefly sum it up, lake turnover is the seasonal mixing of the entire water column. The process of lakes turning over is critical to a lake’s ecosystem, as it’s the turnover period that distributes oxygen throughout the entire water column. Once ice forms across the entire surface of a lake, the body of water is essentially sealed off from atmospheric oxygen exchange and the snow-ice coverage blocks out light that is necessary for aquatic plants and phytoplankton to produce oxygen within the lake. Therefore, oxygen availability becomes more limited during the winter which can pose a threat to aquatic species. In fact, lakes can sometimes experience “winterkill” where the oxygen levels become too low for fish to survive. So, how do aquatic species survive the winter under the ice?

Fish have several adaptations to survive a winter under the ice. Fish are cold blooded, meaning their body temperature is regulated by outside influences and matches their environment. In the winter, they must modify their behavior to regulate and maintain their body temperature. To do this, fish slow down their metabolic processes, such as respiration, digestion and activity level. Some fish species will also enter a state known as “diapause”, where they have an extremely low heart rate. By slowing down their metabolism, fish are able to survive on fewer calories. If feeding does occur, fish will consume a variety of hatching insects and smaller fish.

Where fish overwinter in the water column depends on the fish species. Fish are classified as cold water, cool water, and warm water species. During the winter time, cold water species stay more active throughout the water column and prey on other organisms. Meanwhile, warm water species seek out the warmest water, which is often found at the bottom of the lake. They will hunker down in these areas and enter a state of torpor, where their respiration is reduced and they use as little energy as possible. There are some warm water species that will also burrow into the lakebed for warmth.

Of course, fish aren’t the only species in the lake that have winter survival techniques. Phytoplankton (algae/cyanobacteria) can produce thick-walled resistant cells that will settle to the bottom of the lake where they overwinter. Some phytoplankton remain productive during the winter by utilizing the small amount of light that penetrates through the ice and snow covering the lake’s surface. Zooplankton have similar overwintering strategies as phytoplankton. Zooplankton enter a special resting stage that allows them to survive the winter burrowed in the warmer lake sediments. Once the spring arrives and the lake turns over, and more light is able to penetrate into the water column, these resting stages become active again. As for aquatic plants, many die back during the winter. However, their root systems remain intact and store energy to subsequently produce new vegetation in the spring. And finally for our amphibious friends, they seek out protected areas and burrow down into the sediment, where they enter a state of hibernation.

Winter is a quiet time in and around the lake as species hunker down waiting for the spring. While we humans survive the winter by bundling up and cranking the heat, most of our aquatic friends enjoy a long winter’s nap. Me? Jealous? Well…maybe a little!


Jacquelyn Bellefontaine is the conservation outreach manager for the Lake Winnipesaukee Association. She manages communications and outreach initiatives. Jackie can be reached at

The Lake Winnipesaukee Association is a nonprofit dedicated to protecting the water quality and natural resources of the lake and its watershed. To learn more, visit

Update - Remapping Conway Lake Bathymetry

By Don Yurewicz

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The project to remap water depth across Conway Lake was completed in late 2022.  The project kicked off in July 2021 with an aim to replace the water depth map for Conway Lake that is available from the NH DES with one that is more accurate and detailed.  A portable sonar device that records water depth and latitude/longitude and a sounding line were used in 2021 to collect raw data.  Over the course of the summer and fall over 70 transects were made across the lake collecting 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 were collected in 2022 using a Garmin Echomap depth finder.  It provided more accurate and reliable data that was used to refine the map created in 2021.  Water depth was datumed on a lake level measured on June 25, 2022.  The updated map is available in several formats on the 'Resource' page of this website.

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 look 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 calculated 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 and slow deposition of post-glacial lake sediment. 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 DES map.  These knolls are probably erosional bedrock highs capped with glacial boulders and 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 just over 50’ and sits directly east of Andrews Point.  There is a spot nearly as deep (49’) ENE of Ship Island. 

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