Stormwater runoff: The No. 1 threat to Lake Winnipesaukee’s water quality

More than 90% of New Hampshire’s surface water quality impairments can be traced back to a single source: stormwater runoff. It’s not as attention-grabbing as long-lasting synthetic chemicals, man-made organic chemicals or lead, but it’s arguably one of the most important factors in protecting the long-term health of our waterbodies. But why?

Stormwater runoff is the water that flows off hard surfaces like roads, parking lots, roofs, sidewalks and driveways during rainstorms or snowmelt. Historically, homes and businesses were built with stormwater systems such as gutters, culverts, pipes, and ditches that moved this runoff quickly away from buildings to prevent flooding and damage, often sending it into the nearest waterbody. The theory was simple: “the solution to pollution is dilution.” In practice, this meant treating lakes and streams as convenient sinks for rainwater, road runoff, sediment, and, in some cases, even wastewater.

When water flows over impervious surfaces, it picks up a range of pollutants. This happens because development removes the natural vegetation and porous ground that once absorbed the water, allowing it to collect contaminants like oil, gasoline, pet waste, fertilizer, road salt, sand, and microscopic nutrients such as phosphorus. For a long time, we assumed natural systems could absorb or filter out these pollutants without lasting harm. But now we know what they say about assuming — and we’ve learned nutrients like phosphorus, can build up over time and accumulate in our ecosystems. These pollutants fuel harmful algal blooms and accelerate eutrophication, a fancy word for lake aging.

In just the last 90 days, the National Weather Service station at Lakeport has recorded 15.87 inches of rainfall, which is 5.42 inches above average. That excess water has consequences. Towns are facing damaged or clogged culverts and overwhelmed drainage systems. Homeowners are dealing with washed-out driveways, eroded yards and shorelines, and high water levels are pushing the limits of their waterfronts.

Stormwater runoff doesn’t just damage infrastructure; it harms the health of the very water bodies we rely on for recreation, tourism, wildlife habitat, drinking water, and the local economy. We need to rethink how we manage where that runoff goes. While municipalities are working to install and upgrade systems that help slow and filter stormwater, homeowners and businesses have a big role to play too — especially considering over 90% of Lake Winnipesaukee’s shoreline is privately owned.

But this isn’t just about shoreline residents. Anyone living within the greater Winnipesaukee watershed can help protect the lake. During the next rainstorm, grab an umbrella and rain boots and walk your property. See where the runoff flows. If you're looking for ways to help slow it down and allow it to soak in naturally, consider participating in LakeSmart.

LakeSmart is a free, voluntary, and non-regulatory program developed by NH LAKES to help property owners statewide understand how their everyday actions impact lake health and what they can do to make a difference.

Whether you live on the shoreline or miles away, what happens on your property affects the water we all rely on. By participating in LakeSmart, you can receive personalized recommendations to reduce runoff, protect wildlife habitat, and maintain your property values. If your property already meets lake-friendly standards, or once you’ve made a few simple improvements, you will receive the LakeSmart Award to share with pride. 

On Lake Winnipesaukee, the program is facilitated by the Lake Winnipesaukee Alliance. Our trained Winni Blue Crew offers free, on-site property visits to help you identify practical, often low-cost ways to manage stormwater and protect the lake. To get started, email lakesmart@winnipesaukee.org and take the first step toward becoming a Lake Ally. 

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Bree Rossiter is the conservation program manager for the Lake Winnipesaukee Alliance. She leads the water quality and cyanobacteria monitoring efforts, coordinates the LakeSmart program to promote lake-friendly practices among property owners, and supports community education and outreach initiatives. Bree can be reached at brossiter@winnipesaukee.org. The Lake Winnipesaukee Alliance is the only nonprofit dedicated to protecting the water quality and natural resources of Lake Winnipesaukee and its watershed. To learn more visit winnipesaukee.org.