Climate Change

Climate Change

New Hampshire is getting wetter, but precipitation is coming in fewer storms. This means, rainstorms are bigger and are happening after periods of drought. Under these conditions, the landscape is unable to absorb all the rain at once, so runoff water to our lakes is increasing, bringing in more nutrients to fuel 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 is occurring later in the fall and ‘ice-out’ is happening 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 not only means less opportunity to recreate safely on the ice, it also 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.

Research suggests that warmer winters in New Hampshire are resulting in more sleet and ice—and more road salt being used to address safety hazards on roadways, walkways, and parking lots. This means, more salt pollution to our waters. Research also suggests that increasing salt levels in our lakes may lead to increases in toxins released by cyanobacteria.

Research also suggests that warmer lake water temperatures during the summer can increase how long the relatively cooler, denser bottom waters of our deeper lakes are sealed off from the warmer, more oxygen-rich waters above. The longer the bottom waters aren’t able to mix with the waters above during the summer, more and more oxygen will be used up in the bottom waters by chemical and biological processes. 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