Understanding Lake Winnipesaukee Water Levels

Why does the water rise and fall? Who controls the dam? Everything you need to know about New Hampshire's largest lake and how its levels are managed.

Why Do Water Levels Change?

Lake Winnipesaukee's water levels fluctuate throughout the year due to a combination of natural factors and deliberate human management. Understanding these patterns helps lakefront property owners plan for seasonal changes and protect their docks, boats, and shoreline structures.

Natural Factors

• Precipitation: Rain and snowmelt are the primary natural inputs. An inch of rain over the 363-square-mile watershed can raise the lake level by 5 inches when the soil is saturated.
• Evaporation: During warm summer months, the lake loses water to evaporation, contributing to gradual level drops.
• Spring Runoff: Snowmelt in March and April can cause rapid level increases, sometimes bringing inflows of 8,000 to 10,000 cubic feet per second.
• Seasonal Patterns: By mid-fall, the lake is typically about 15 inches below its springtime full level due to summer evaporation and outflow.

Human Management

The Lakeport Dam in Laconia controls the outflow from Lake Winnipesaukee, making it the primary tool for water level management. The New Hampshire Department of Environmental Services (NH DES) Dam Bureau operates the dam to balance multiple competing interests.

The Lakeport Dam: Past and Present

Who Controls the Dam Today?

The New Hampshire Department of Environmental Services (NH DES) Dam Bureau is responsible for operating and maintaining the Lakeport Dam. Their Operations and Maintenance Section manages water levels at the state's largest lakes, with decisions guided by multiple competing needs.

Funding the Dam

Under state statute, downstream hydropower plants on the Winnipesaukee and Merrimack Rivers pay Water User Fees for the storage and release of water from Lake Winnipesaukee. These fees fund the operation and maintenance of the dam.

Seasonal Water Level Management

Spring (March - May)

The goal is to reach "full pool" - elevation 504.32 feet - by Memorial Day for the summer recreation season. Dam operators carefully manage releases to accommodate spring snowmelt and rainfall while gradually raising the lake level.

Summer (June - September)

During boating season, levels are maintained between 502.80 and 504.32 feet. A minimum release of 250 cfs continues to support downstream needs. Despite this careful management, the lake typically drops about 10 inches over the summer due to evaporation and required releases.

Fall (October - November)

Unlike most New Hampshire lakes, Winnipesaukee is not deliberately drawn down in fall. However, the lake naturally drops as releases continue. After Columbus Day, releases are temporarily reduced to 30-50 cfs for about two weeks to allow maintenance of downstream dams and hydropower facilities.

Winter (December - February)

The lake continues to drop through winter, reaching its lowest point - about 2 feet below summer full pool - by early March. This "drawdown" serves multiple purposes: it reduces ice damage to shoreline properties, gives homeowners a chance to make waterfront repairs, and creates capacity to absorb spring snowmelt and rainfall.

Balancing Competing Interests

Dam operators must carefully balance many different needs:

• Recreation: Boaters need adequate water depth from Memorial Day through Columbus Day
• Hydropower: Downstream plants have legal rights to minimum water releases
• Flood Control: Winter drawdowns create capacity for spring runoff
• Property Protection: Levels that are too high or too low can damage docks and shorelines
• Downstream Communities: Releases support water levels in Silver Lake and help the Winnipesaukee River Basin Wastewater Treatment Plant meet its permit requirements
• Fisheries: Minimum flows support fish populations in the Winnipesaukee River

Wildlife Considerations

Water level management must also account for the lake's wildlife, which is protected by state and federal regulations:

• Loons: These iconic birds return to the lake in spring and build nests close to the shoreline. They need stable water levels through May and June to avoid flooding or stranding their nests.
• Lake Trout: Spawning occurs around Halloween, requiring stable levels to avoid stranding eggs on exposed shoreline.
• American Eels: From mid-August through mid-November, eels migrate out through the dam on their way to the sea. Releases must be carefully managed to avoid harming them during this critical period.

Extreme Weather Events

During major storms or rapid snowmelt, dam operators face difficult decisions. Inflows into Lake Winnipesaukee can peak at 8,000 to 10,000 cubic feet per second, but if releases exceed 2,000 cfs, they begin causing flooding to low-lying properties downstream on the Winnipesaukee River.

This means that during extreme events, some flooding is inevitable - either on the lake itself (if releases are restricted) or downstream (if releases are increased). Operators must balance these competing risks in real-time.

Where Does the Water Go?

All of Lake Winnipesaukee's water flows through a single outlet: into Paugus Bay, through the Lakeport Dam, into Opechee Bay, then into Lake Winnisquam and the Winnipesaukee River. The river eventually joins the Merrimack River, which flows through Massachusetts to the Atlantic Ocean.