For many, summer is the time to go to the beach. But maybe not every beach if you don't want to swim in harmful bacteria.

From late May to early September, New Hampshire's Beach Inspection Program monitors public beaches for fecal bacteria. And with reports from residents, the state also tracks cyanobacterial blooms, growths that can be dangerous to people and pets.

Current information on both types of danger can be found online at Healthy Swimming MapperAs of Tuesday afternoon, the following locations were marked:

• A cyanobacteria warning has been in effect for Lake Kanasatka in Moultonborough since June 26.
• A cyanobacteria warning has been in effect for Mill Pond in Alton since June 14.

It is important to note that just because a body of water does not have an advisory does not mean it is safe. Beaches are not tested every day, and the state relies on residents to report potential cyanobacterial blooms, which is an online form.

Cyanobacteria warnings mean that residents should be “on alert” for a possible cyanobacteria bloom, according to the Department of Environmental Services. Warnings mean that cyanobacteria have been found at a concentration where harmful toxins could be present and threaten public health.

According to DES, a fecal bacteria warning is issued when a water sample “shows levels that exceed state standards and indicate unhealthy bathing conditions.”

The summer months can pose the greatest risks in aquatic environments due to the large number of swimmers and higher temperatures that can encourage bacterial growth. Here's what you need to know before a busy beach holiday.

Fecal bacteria

If goosebumps are not enough to avoid fecally contaminated water, these bacteria can, according to the US Environmental Protection Agency.

New Hampshire has monitored ocean beaches since 2003and samples them regularly from Memorial Day through Labor Day. DES says only a subset of freshwater beaches are sampled — usually monthly — because there are so many of them. State parks are prioritized and sometimes sampled more frequently.

This pollution is a nationwide problem. About half of the Environment Americaa nonprofit environmental organization, encountered potentially health-threatening levels of fecal contamination on at least one day in 2022.

In 2023, feces warnings were issued for five of New Hampshire's 16 coastal beaches, said Michele Condon, the beach inspection program coordinator. There were 11 warnings in total, with some beaches having more than one during the summer.

By comparison, there were a total of 14 coastal warnings in 2022, 18 in 2021, 10 in 2020 and three in 2019, she said.

There is always some risk of pathogens being in the water, but that risk is greater after heavy rains, Condon said. These significant storm events, seen in the 2023 swim season, “can bring in potential stormwater and increase bacteria levels,” she said.

In addition to rainwater, Condon named a number of other sources of fecal contamination: “waterfowl (especially geese), domestic animals, defective sewage systems or improperly functioning toilet facilities, and a high density of recreational workers.”

Cyanobacteria

Cyanobacteria – sometimes called blue-green algae, although they are not algae – are often toxic.

They thrive on sunlight, warmth and nutrients, making the summer months an ideal feeding ground. As climate change causes temperatures to rise, beachgoers can expect to be greeted by these unpleasant visitors more often.

DES recorded the most lake blooms ever in 2023, affecting 47 lakes. This reflects a global trend toward more frequent lake blooms, but also greater public awareness leading to more reporting.

Cyanobacterial blooms can be blue, green, yellow, white or brown and look like spilled paint, foam or stains.

They often produce toxins that can cause a number of serious health problems, including skin rashes, fever, headaches, mouth blisters, vomiting, acute liver damage and more, according to the Department of Environmental ServicesThey can sometimes also cause neurological problems such as numbness and seizures.

If the water looks suspicious, DES recommends residents stay outside and report details to the state so others can be warned.

You can register for water-specific Notes and nationwide updates on-line.