Early in the morning most days, Ryan Wood wades out into the cold water at Fishermen’s Beach.

“I basically go out each morning, usually at Fishermen’s Beach and sometimes at King’s Beach, go into the water and get samples,” said Wood.

Wood is spending his summer interning with the Swampscott Board of Health. His main responsibility is to collect, test and analyze ocean water samples. After grabbing the samples, the level of bacteria the water contains is measured.

According to the Massachusetts Department of Public Health, water is considered safe when bacterial levels are at or below 104 colony-forming units per 100 milliliters (cfu/100 ml). An additional measure, the geometric mean, reflects average water quality over the past month, based on the five most recent test results. For marine beaches, the allowable geometric mean is 35 cfu/100 ml. 

The process aligns with a lot of the coursework Wood has completed during his time as a student at University of New England in Biddeford, Maine. Wood will be a senior this fall.

“The primary idea of (sampling) is to have the data available for people to use for public health related concerns,” said Wood.

One source of troublesome bacteria comes from sewage in surrounding areas. Along with ocean water, Wood collects samples from different culverts as well.

Bacteria levels tend to spike just after heavy rain events. Thunderstorms and rainfall can sweep trash and chemicals into storm drains and other access points to the ocean, causing bacteria levels to rise.

Signs posted at beaches around town recommend not swimming for 48-72 hours after precipitation.

Most samples that have been collected this summer have a low, unproblematic level of bacteria, according to Wood.

“Most of the time it’s been at a safe level,” said Wood. “Usually after rain events we’ve seen unsafe days so far.”

Water sampling and testing, as well as making results available, play a role in raising awareness around the way popular beaches have water that can have varying levels of pollution from day to day, said Wood.

“People want to use the beaches to swim,” said Wood. “It’s important for them to understand what the health risks are. It’s good to be transparent about the beaches they are swimming in.”

Each week, water quality updates can be viewed on the Swampscott Tides’ Summer Shore Report, which is published on Thursdays.