A New Hampshire lake at sunset


Here are some questions people often have about lakes. If you have a question that is not listed, be sure to check out our article library—click here.

You can always contact us with your question too! Just email or call 603-226-0299.

You might think that a waterbody named “Lake Such-and-Such” would be bigger and deeper than one named “Pond Such-and-Such.” This is isn’t always the case! In New Hampshire, naming lakes and ponds was unscientific—most were named by the early settlers who lived nearby. To learn more, click here.

Lots of things—thank you for asking! Two of the biggest threats to New Hampshire’s lakes are the spread of invasive species and polluted runoff water from the landscape. If you boat, always clean, drain, and dry your boat, trailer, and gear between uses in different lakes. If you live near a lake, add shrubs and groundcover, and other lake-friendly landscaping features, to your property to soak up runoff. There are several other things you can do. To learn more, click here.

Generally, yes, it is safe to swim in most of New Hampshire’s lakes most of time. But, sometimes swimming in the lake can pose health problems. Swimmers can get sick when high levels of bacteria or harmful algal blooms are in the water. Many public swimming areas on New Hampshire’s lakes are tested for bacteria and advisories are issued when levels are high. But, not all areas of all lakes are tested. Be sure to look before you leap into the water. If the water looks like someone dumped pea soup, antifreeze, or blue-green paint into it, don’t leap in. Avoid contact with the water and report what you see to the New Hampshire Department of Environmental Services at (603) 848-8094. Keep your pets out of the water, too. To learn more, click here.

Once lake water has been treated to remove bacteria, typically it is safe to drink. There are several types of residential lake water treatment systems available. But, don’t panic if you swallow a mouthful of water while swimming—a few gulps won’t likely make you sick.

Green or blue-green scum on the top of the lake or chunks floating near the surface are likely cyanobacteria (bacteria that act like algae, commonly referred to as ‘harmful algae’). This type of material can be hazardous to your health. If you see green or blue-green scum or chunks in the lake, do not walk or swim in the water, do not drink the water, and do not let your pets into the water. Contact the New Hampshire Department of Environmental Services at (603) 848-8094 to report it. To learn more, click here.

You may find a billowy mass of what looks like green cotton candy in the lake during mid-summer after a long hot spell or big rainstorm. These masses are made up of hair-like strands of thousands of individual green algae cells connected end-to-end. These growths are not harmful to humans. But, they indicate there may nutrient pollution in the lake. To learn more, click here.

This could be a rare form of colony forming cyanobacteria that grows in the shallows of low-nutrient lakes. Sometimes referred to by the nickname troll jelly, Nostoc is often described as marble shaped “balls of jelly” that can vary in size. Nostoc is not an indicator of water quality concerns and ancient colonies of Nostoc have been recording growing in the arctic where the cold water is actually too low in nutrients for many organisms to live there! While Nostoc is not a concern for swimming it should not be consumed by humans or animals and has been linked to amyotrophic lateral sclerosis (ALS) syndrome in other countries who actually eat it as a delicacy. If you spot this rare cyanobacteria in the water please take a photo and send it to info@nhlakes.org (or NHDES Beach Inspection Program at beaches@des.nh.gov)!

Poke the sheen with a stick. If the sheen breaks apart and does not come back together, then it is from natural sources and there’s no need to worry. If the sheen swirls back together as soon as you take the stick out, the oil is likely due to a man-made petroleum product. Contact the New Hampshire Department of Environmental Services to report any potential petroleum release. For reporting information, click here.

During late-spring, many of our lakes become dusted with pine pollen which is typically bright yellow. Wind and wave action blow the pollen into cove areas where it collects and forms thick mats along the shoreline. After becoming waterlogged, the pollen will sink to the lake bottom and decay naturally.

Lake foam is usually a natural phenomenon. When plants, algae, and fish die and decay, natural oils are released into the water. These oils reduce the attraction of water molecules for each other. This allows wind and waves to mix air into the water, causing foam to be produced. Foam collects along windward shorelines. It is usually easy to tell if foam is natural or not—a quick test is to smell it. If the foam has a floral or perfume-like aroma, then it is likely caused by a detergent. If the foam has a fishy or earthy aroma, then it is probably natural. Also, natural foams are generally off-white, tan, or brown in color instead of bright white. To learn more, click here.

Seeing orange or reddish-brown clumps, fluff, or slime in streams or along the shoreline can be alarming. But, don’t worry it’s not a human health threat. This material is made by bacteria that eat iron. Iron is found naturally in the soil. If you don’t like the look of it, you may be able to prevent it. For more information, visit the New Hampshire Department of Environmental Services—click here.

A lake with clear blue water does not contain a lot of particles floating in it. The blue wavelengths of sunlight are relatively long and reach deeper into the water. The darker the blue, the deeper the water.

A lake with green water typically has a lot of algae growing in it. Algae and other microscopic organisms have pigments that are usually green in color. When there is a lot of algae, whole areas of a lake can be covered with a colored bloom. A lake can also contain red or brown algae blooms.

Water that is clear and brown in color is usually no reason for concern. The dark color is probably due the natural materials released by decomposed plants, leaves, and bark in the water.

Water that has a milky coffee-colored look to it usually contains a lot of soil particles that haven’t fallen down to the lake bottom yet. This could be caused by winds that stir up the lake bottom. Most often, milky coffee-colored water is caused by runoff water that has eroded soil off of the landscape and into the lake, and is cause for concern.

Thanks for being on the lookout! Here’s what you can do to make sure you get the right information to the right people:

  • Note the location of where you found it by referencing a point on shore.
  • Collect a sample of what you found. For plants, be sure to get a piece of the stem and the leaves.
  • Share what you found with the New Hampshire Department of Environmental Services (DES) in one of the ways listed below. Don’t forget to include information about where you found it (lake, town, location in the waterbody) and your contact information (your name and phone number).
    • Mail the specimen to Amy Smagula, DES, P.O. Box 95, Concord, NH 03302-0095. (Wrap it in a moist paper towel and place in a sealed bag.)
    • Take a digital photo and email it as an attachment to Amy.Smagula@des.nh.gov.
    • Drop it off at the DES Jody Connor Limnology Center at 29 Hazen Drive in Concord, New Hampshire.
    • DES will identify the plant and notify you of its identification. They will then take any appropriate management strategies.

Removing dams and trapping beavers are not long-term solutions. The installation of a water flow device (commonly called a ‘beaver deceiver’) can solve water level problems caused by beavers. Water flow devices can be installed without a state permit if certain conditions are met. For more information, visit the New Hampshire Fish and Game Department—click here

Remove the welcome mat! You maybe unwittingly encouraging these beautiful, but messy birds, to visit your property. Canada Geese need fresh water for resting and nesting and tender young grass for food. A green grassy lawn that extends to the lake’s edge provides excellent habitat for Canada Geese. Make your property unattractive to them. Plant a row of native shrubs at least three feet tall along the shoreline. Overlap two rows so people can access the water but so geese can’t see the water from the lawn. For more information, click here.

NH LAKES occasionally gets calls from concerned individuals who have observed dead fish in the lake or washing up on shore. While alarming, fish kills do not always indicate that the water is polluted or unsafe for swimming and recreation. With that said, it is important to keep people and pets out of the water until you know for certain. For more information, click here.

Maybe. Under New Hampshire state law, there is a 250-foot protected area around lakes. Some forms of development are restricted in this area and some are not allowed. Other activities require a state permit. For more information, visit the New Hampshire Department of Environmental Services—click here.

Technically, yes, but it is not recommended. Some of the chemicals used to pressure-treat wood can be toxic to humans and wildlife. Cedar, metals, plastics, and composite materials are recommended instead. For more information, visit the New Hampshire Department of Environmental Services—click here.

Maybe. A state permit is required for the construction or replenishment of a beach with sand. Sand placed along the shoreline can wash into the lake and increase plant, algae, and bacteria growth, reduce water clarity and depth, and smother fish spawning sites. If you want a sandy beach, consider getting approval for a perched beach. For more information, visit the New Hampshire Department of Environmental Services—click here.

Probably not, but you might be able to slow down the accumulation of muck. Muck is typically made up of decaying leaves, plants, and algae. The formation of muck happens naturally over time, but human activity can speed it up. To slow down the process, don’t dump leaves or grass clippings into the lake. And, during periods of low water, hand-remove dead plants and leaves from dry areas of the lake bottom.

No. In New Hampshire, only trained, licensed applicators with a special permit can use any kind of chemical to control plant growth in the water. If plants completely block your access to the water, you are allowed to hand remove small areas by docks and swim areas. It is best to remove the plants by cutting the stems and leaving the roots in the lake bottom.

In most New Hampshire towns, it is legal to launch fireworks. But, there are growing concerns about the potential for fireworks to pollute lakes and groundwater. There are several practices recommend to minimize the impact of firework displays on the quality of lakes and groundwater. For more information, visit the New Hampshire Department of Environmental Services—click here.

The short answer is that lakefront property owners have a right under New Hampshire state law to ‘wharf out’ onto public waters. The actual type, shape, size, and location is subject to permitting by the New Hampshire Department of Environmental Services. For more information visit the New Hampshire Department of Environmental Services—click here.

A state permit is required to rototill a beach. A New Hampshire Department of Environmental Services Wetlands Permit By Notification (PBN) for beach replenishment / maintenance would be appropriate to obtain the necessary approval for the project. For the Beach Replenishment Permit-by-Notification Checklist—click here.  For the Wetlands Permit-by-Notification—click here.

Pesticides are toxic to aquatic life. Within 50 feet of the reference line of public waters, pesticides can only be performed by professionals who have been licensed by the New Hampshire Department of Agriculture. While there are essential oil-based “minimum risk pesticides” available that can be applied without a license, application best practices are still crucial. Shorefront property owners should always work with a licensed pesticide applicator. NH LAKES does not recommend that any (traditional or minimum risk) pesticides be used within 50 feet of the water.

Golf balls can harm aquatic life and release toxic metals and microplastics into our waters as they break down over time. Littering is illegal in New Hampshire, and hitting a golf ball into a lake is considered littering. To read more about golf balls in waterbodies—click here.