Water Quality

Water Quality in New Hampshire's Lakes

New Hampshire is home to approximately 1,000 lakes and ponds—some of the cleanest and healthiest lakes in the country. However, there has been a downward trend in water quality in many of our lakes over recent years.

What drains from the land into the water is a main factor affecting the health of our lakes.

The New Hampshire Department of Environmental Services publishes a report every two years detailing the condition of New Hampshire’s lakes and ponds. It analyzes how well they support aquatic life and recreational activities. Some waterways are classified today as being impaired, meaning they are not healthy enough to support a variety of plants, animals, and uses.

You can learn more about the NHDES analysis here. 

Threats to Water Quality

Image of a cyanobacteria bloom on a lake


New Hampshire’s lakes have seen a record number of toxic cyanobacteria blooms for the past three summers. These blooms can produce toxins that make people, pets, and wildlife sick.

Climate Change

New Hampshire is experiencing increased precipitation, but it’s happening in fewer storms. This means that larger rainstorms occur after dry periods. As a result, the land can’t soak up all the rain at once, leading to more runoff water and nutrients entering our lakes that contribute to the growth of native and invasive plants, algae, and toxic cyanobacteria.

Hero Photo for Climate Change, features dry and cracking soil with one small plant.
Image of water running and streaming into larger and separate body of water.

Polluted Runoff Water

The water quality of a lake is primarily determined by what flows into it from the surrounding landscape (the watershed).

Our lakes are home to many different kinds of plants and animals that are good for the lake. But, some species are harmful to our lakes.

Image of young girl swimming with invasive species of plants in a lake