SMITHFIELD, R.I. — At Slacks Reservoir on a sunny June day, people gathered on what is known as Little Beach to fish.

“No, no, no,” Gary Rose, 71, said, shaking his head when asked if he and his grandchildren would be eating their catch. “I wouldn’t.”

The Rhode Island Department of Environmental Management issued an advisory for the reservoir’s beach in early May because a harmful algal bloom had formed on the waterbody. With that advisory, the state warns against coming into contact with the water or eating what’s swimming in it.

The toxins made by the algae can cause a range of symptoms, from itchy skin and eyes to nausea and vomiting, and, in the most severe cases, liver failure.

The advisory was the first of the season, one of two posted by DEM since the start of spring.

On the day Rose visited the pond with his grandkids, it looked clear, likely because it had already been treated to remove the photosynthesizing, toxin-producing organism from the water, but DEM had not yet lifted its advisory.

“You can see [blue-green algal blooms] pretty clearly. They say it’s like pea soup, and it really is,” said Rose, who is from Cranston. He is already well acquainted with the algae because, last summer, he and his grandkids had to try about a dozen different fishing spots throughout the season as beach after beach came under algal bloom advisories.

Warmer, longer summers and less winter ice cover due to climate change are likely making blue-green algae blooms more common, according to Brian Zalewsky, an environmental scientist for DEM’s Office of Water Resources.

Although they are becoming more familiar to Rhode Islanders, Zalewsky explained the blooms aren’t always easy to spot, and citizen reporting is a crucial part of the state’s monitoring program.

When and where do blooms happen?

Cyanobacteria — also known as blue-green algae because of the bright colors they can create when they form large blooms — are found naturally in fresh water but become a problem when they overproduce and release chemicals that can make people and animals sick.

Usually, DEM starts to see the blooms in the summer months, as water temperatures rise, Zalewsky said, although that’s been changing.

The monitoring season used to start in June but has shifted to early May. DEM posted its first bloom advisory this year on May 9, and in at least one instance a few years ago, it posted an advisory in April.

On the tail end, the bloom season is also extending. “We’ve been out later and later in the season,” Zalewsky said. “We’ve seen some blooms through the ice.”

When the season starts, DEM monitors about two dozen waterbodies where it “seems like every year they experience cyanobacteria blooms,” said Zalewsky, often because of high nutrient levels that feed the cyanobacteria to grow into big, soupy patches.

Slack Reservoir; the ponds at Roger Williams Park in Providence, including Mashapaug; Almy Pond in Newport; and Spectacle and Blackamore ponds in Cranston are among those with the highest number of bloom advisories over the past 10 years.

What does a bloom look like?

Blue-green algal blooms can look different based on conditions and the types of bacteria in a bloom, according to Zalewsky, but there are some traits to look for.

There’s an “odd deep/bright green or blue color” to many blooms, he said. “It just doesn't look right, just doesn't look natural.”

The blues can look like spilled paint with “cotton balls” of bright green.

“So, it can be pretty dramatic,” Zalewsky said, “and then sometimes it's not so dramatic.”

Some cyanobacteria can change their height in the water, sinking deeper below the surface, making the water look murky.

Poor water transparency can hint to a bloom, he said.

Common mistaken identifications of cyanobacteria blooms are often non-harmful green algae, which can still obstruct activity like boating, or pollen floating on the surface.

How do you report a potential bloom?

To let the state know a bloom might have erupted on one of its ponds, lakes, or reservoirs, DEM and the Rhode Island Department of Health (RIDOH) share an email hotline, where residents can send descriptions, photos, and locations of potential blooms.

Jillian Chopy, assistant health program administrator at RIDOH’s Beach Monitoring Program, encouraged members of the public to submit information, especially photos, even if they aren’t sure that it’s a bloom.

Once RIDOH and DEM receive a possible bloom, DEM samples and tests the water at RIDOH's state health laboratory, and if there is a toxic bloom, the agencies jointly issue an advisory.

RIDOH sends out press releases and informs the organization that oversees the waterbody — usually a neighborhood association or a municipality.

For beachgoers, in addition to any visible blooms on the water, red warning signs from RIDOH should let them know that it’s not safe to come into contact with the water. Chopy also noted that just because a bloom isn’t visible or located directly in a recreating area doesn’t mean that the toxins they produce haven’t infiltrated the whole waterbody. Advisories will note whether a closure is only for a section of the beach or the entire area.

If a boater or swimmer thinks they have touched or swallowed some of a harmful algal bloom, and they are starting to show symptoms, Chopy said to first reach out to a health care provider (or vet in case of a pet exposure) and then let RIDOH know, either through the blue-green algae email or the beach monitoring program phone line at 401-222-7727.

On top of the state’s hotlines, The Nature Conservancy in Rhode Island is helping to monitor the bloomWATCH app, which lets people record observations in their neighborhoods.

Like the state email, sometimes observed blooms in the app are actually just pollen or regular algae, according to TNC coastal restoration scientist Heather Kinney.

Kinney said TNC errs on the side of caution when passing on photos to the experts at DEM, only weeding out clearly unrelated observations.

“Sometimes people just take photos of trash,” she said, laughing, “like, ‘Oh, look, there's trash here.’ Like, that's not what this is for. But thank you.”

How can blooms be prevented?

If the DEM’s Zalewsky had a magic wand, he would start with wrangling the excessive runoff that carries nutrients into the water, supplying the cyanobacteria with the energy to grow into large masses.

Reducing fertilizer use, maintaining vegetation along the sides of waterbodies, and installing rain gardens are all ways of preventing or lessening the nutrients that enter the environment.

But the problem would likely still linger, long after the best practices were put in place.

“An urban lake or pond that's been receiving runoff for decades, 30, 40, 50 years,” he said, “even if you kind of cut that off, there's still so much phosphorus and nutrients that are in the sediments.”

The nutrients can get rereleased in a cycle that can also last decades and decades.

“It's a challenging problem, for sure,” he said.

Still, there are some success stories. Yawgoo Pond in South Kingstown, for instance, has seen fewer blooms since the identification and mitigation of specific nutrient sources.

While the long process of restoring Rhode Island’s freshwater bodies is ongoing, the monitoring program is the front line for protection — and the season has just begun.

“We'll be chasing these things around all summer,” Zalewsky said.

Editor's note: This story was updated at 11:13 a.m. on June 18.