Climate Change

Climate Change

Climate Change and New Hampshire's Lakes

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. 

Our changing climate is negatively impacting the water quality of our lakes in New Hampshire in many alarming and interconnected ways.

New Hampshire is getting warmer. ‘Ice-in’ on our lakes occurs later in the fall, and ‘ice-out’ happens earlier in the spring. Research suggests that over the past approximately 100 years, the period of ice cover on New Hampshire’s lakes has decreased by one to two weeks.

A shorter period of ice cover on our lakes means less opportunity to recreate safely on the ice and negatively impacts lake health. Less ice on the lake for less time means a longer growing season for plants (including invasive plants), algae, and toxic cyanobacteria.

Warmer winters in New Hampshire are resulting in more sleet and ice. As a result, more road salt is being used to address safety hazards on roadways, walkways, and parking lots. This means more salt pollution in our waters. Increasing salt levels in our lakes may increase toxins released by cyanobacteria.

Warmer lake water temperatures during the summer can increase how long our deeper lakes’ relatively cooler, denser bottom water is sealed off from the warmer, more oxygen-rich water above. The longer the bottom water cannot mix with the water overhead, the more oxygen will be used up by chemical and biological processes during the summer. If all the oxygen gets used up, a chemical reaction may occur that releases nutrients from the bottom sediment into the water. When the lake finally fully cools down in the fall and all the water in the lake mixes together from top to bottom, these extra nutrients may cause late-season toxic cyanobacteria blooms.

Threats to Water Quality


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.

Polluted Runoff Water

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


nh lakes runoff

monitor manage invasive species nh lakes

Invasive Species

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.