Lake Winnipesaukee’s water levels: From spring highs to fall lows

What a difference a few months can make on Lake Winnipesaukee.

In May, the lake climbed nearly eight inches above full, bringing submerged docks, vulnerable shorelines and plenty of questions about why more water could not simply be released. Today, we are at the other end of the spectrum. On Friday, Winnipesaukee measured 502.85 feet, nearly 18 inches below full lake and just six-tenths of an inch above the lower end of the New Hampshire Department of Environmental Services’ summer recreation operating range.

It is a dramatic swing, but it also illustrates just how complicated managing the water level of Lake Winnipesaukee can be.

The NHDES Dam Bureau has a long list of variables to consider throughout the year: rainfall and forecasts, snowpack, runoff and soil moisture, evaporation, downstream flooding, recreation and navigation, shoreline property, hydropower operations, downstream flow requirements and aquatic habitat. And on a lake this large, changes cannot happen overnight.

Throughout the summer, a minimum discharge of 250 cubic feet per second is maintained at Lakeport Dam to meet deeded water rights dating back to the 1800s. That equals roughly 112,000 gallons per minute. During dry periods, that release can outpace the amount of water flowing into the lake. Combined with normal summer evaporation, NHDES says Winnipesaukee will typically drop 12 to 15 inches over the course of the summer.

This year, the decline has been greater than that typical summer drop, leaving the lake very near the bottom of its summer operating range.

Water levels matter for more than just docks and boating. Low water can expose rocks, shorelines and other hazards that were safely submerged earlier in the season. It can also affect aquatic habitat.

Around late October and November, lake trout move into areas with rocky bottoms to spawn. Their eggs settle into spaces between the rocks, where they remain through the winter before hatching. That means water levels after spawning matter. If the lake drops too far, eggs deposited in the shallowest areas can be exposed to air or freezing temperatures before they hatch.

Despite what we often call a “fall drawdown,” Winnipesaukee is not managed like many smaller lakes that are deliberately lowered several feet each fall. Around Columbus Day, flows at Lakeport are reduced for roughly two weeks to allow maintenance along the Winnipesaukee River. After that, releases are adjusted based on lake levels, runoff and weather conditions. The lake’s deepest seasonal drawdown comes later, with a target of approximately 502.32 feet, two feet below full lake, by late winter.

This spring, the challenge was high water. Today, we are near the bottom of the summer operating range. Both are reminders that managing Lake Winnipesaukee is a year-round balancing act shaped by rainfall, runoff, evaporation, downstream needs, recreation and the ecology of the lake itself.

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Bree Rossiter is the associate director of the Lake Winnipesaukee Alliance, the only nonprofit dedicated to protecting the water quality and natural resources of Lake Winnipesaukee and its watershed through science, education, advocacy, and collaborative solutions. Her work focuses on advancing long-term watershed protection initiatives and connecting science with practical solutions to help preserve the lake for future generations. To learn more, visit winnipesaukee.org.