Signs of Decline: State of the Lake Assessment
For Immediate Release
New Report finds Lake Winnipesaukee’s Water Quality Is Declining
Loss of water clarity, rising phosphorus levels and increasing cyanobacteria signal the need for action to protect New Hampshire’s largest lake
Meredith, N.H. — [September 24, 2026] — The Lake Winnipesaukee Alliance (LWA) today released Signs of Decline: Assessing the State of Lake Winnipesaukee, the most comprehensive analysis to date of the lake’s water quality and watershed health.
The findings carry both a warning and an opportunity: Lake Winnipesaukee remains a remarkably clean and beautiful lake, but decades of water-quality data show that its condition is deteriorating.
Among the assessment’s most significant findings:
- Water clarity is declining. Long-term monitoring shows that the lake is becoming less clear, an important indicator of changing water quality.
- Phosphorus levels are increasing in the lake. Phosphorus is the nutrient that directly fuels excessive algae and cyanobacteria growth in freshwater lakes. Even relatively small increases can have significant consequences over time.
- Cyanobacteria abundance is increasing. Excessive cyanobacteria can result in blooms, as occurred in 2024, that impair recreational use of the lake and, under certain conditions, produce toxins harmful to people, pets and wildlife.
Taken together, these trends provide compelling evidence that Lake Winnipesaukee is under increasing pressure from development and human activity throughout its watershed.
“The science is clear,” said Eric J. Siy, Executive Director of the Lake Winnipesaukee Alliance. “Lake Winnipesaukee is still a magnificent lake, but its water quality is declining. We have an opportunity to address these problems now before they become far more difficult and costly to solve.”
The assessment identifies phosphorus pollution as one of the central threats to the lake’s future. Phosphorus enters the lake from a variety of sources, including stormwater runoff from roads, driveways and developed properties; erosion and disturbed soils; aging or poorly functioning septic systems; and other activities throughout the watershed.
As development increases, more forested land is replaced by roofs, pavement, lawns, roads and other surfaces that accelerate the movement of stormwater and pollutants into streams and ultimately the lake.
The result is a gradual change in the lake’s natural balance.
For residents and visitors, the most visible signs can be reduced water clarity – more than 8 ft. since the 1980s – and the emergence of cyanobacterial blooms, most extensive in 2024. But LWA cautions that these are symptoms of a larger process that, if allowed to continue into the future as the Assessment projects, could fundamentally alter the character of Lake Winnipesaukee.
“This assessment is not saying that Lake Winnipesaukee is a polluted lake. It isn’t,” said Mark Ishkanian, Chair of the LWA Board of Directors. “It is telling us that the direction of change is unmistakable—and that waiting until the damage is more obvious would be a serious mistake.”
The assessment is intended to establish a scientific baseline that informs and engages the many interests who care about and depend on a clean, clear lake. Equipped with this common understanding, the Alliance will work with these interests as partners in solving the problems identified by the science and securing the future health of the lake.
“We were honored to partner with LWA on this landmark assessment,” said Forrest Bell, Owner and CEO of FB Environmental Associates. “The breadth and depth of the science provide the understanding needed to make informed decisions and address threats to water quality before they intensify.”
LWA is already applying the science to advance responsive new programs aimed at reducing the amount of phosphorus and other pollutants reaching the lake. In particular, this work focuses on identifying and curbing stormwater runoff in high-priority locations. It also includes working with property owners to improve septic system maintenance and, where needed, upgrading faulty systems.
LWA is also working with municipalities and private contractors to reduce excessive road salt use, considered the “acid rain of our time” given the severity of its impacts on lake and watershed health. Finally, LWA will be working with public and private interests to prevent more aquatic invasive species from entering the lake, another significant threat highlighted in the Assessment.
As needed to drive progress at the speed and scale required, LWA’s comprehensive new programs engage property owners, businesses, and communities throughout the watershed as contributing partners, with each having a specific role in protecting the lake.
The steps now needed to succeed are presented in LWA’s Legacy Strategy. Guided by the science, the Strategy’s Blueprint for Lasting Protection outlines the actions required to reduce pressures on the lake and increase its resilience to decline. As highlighted in the Blueprint, new digital tools and a data dashboard tracking progress will keep people informed in this data-driven pursuit of protection.
“We know more today about what is happening to Lake Winnipesaukee—and what we can do about it—than ever before,” Siy said. The science gives us a clear path forward. Now we need everyone who cares about this lake to join us in protecting it.”
Ishkanian said the assessment should be viewed as a call to action rather than a prediction of inevitable decline.
“We still have time to change the trajectory of Lake Winnipesaukee,” he said. “We can either watch these trends continue for another 10 or 20 years, or we can act now to ensure that our children and grandchildren inherit the same clean, clear lake that generations before us have enjoyed.”
The complete State of the Lake Assessment and additional information about LWA’s lake protection programs are available at: trends.winnipesaukee.org
