It’s not easy work: wearing waders and boots on a 90-degree day, cutting the stalks off invasive plants called phragmites with pole saws.

Meanwhile, another group is removing the roots of the plants, also known as common reeds, so they won’t grow back.

"That’s what’s at the very bottom of the basin, and it weighs a ton,” said Boris Santos, intern stewardship coordinator for the nonprofit environmental education organization NYC H2O.

The group has turned the former Ridgewood Reservoir on the Brooklyn-Queens border into an environmental classroom for 16 summer interns.

The work the interns are doing, sometimes up to their waists in water and muck, is pivotal to the health of the body of water. The Ridgewood Reservoir once supplied water to Brooklyn in the 19th and 20th centuries, and now has been transformed into a freshwater pond within the city’s Highland Park.

“It is critical, yeah, without their help, this won’t happen,” Zihao Wang, a forester with the New York City Department of Parks and Recreation, said of the interns.

The students are paid interns, working at the reservoir twice a week and at other locations two other days, including NYC Parks nurseries. That’s where native plants are grown that can be replanted at the reservoir.

“It’s a good thing to do. This is an invasive species, and it takes away a lot of the biodiversity from this park and a lot of other places around the state, so it’s a good thing to do, nice to get outside and help the community,” Jordan Casalinova, an intern from Brooklyn, said.

Intern Jonell Newell, of Jamaica, Queens, aspires to be an attorney, and says the experience is teaching her a lot about teamwork. 

“I’m usually doing things by myself, but meeting all these great people — they are so nice, this is amazing,” Newell said.

A few things happen as part of the six-week program: Students are introduced to green jobs, and the pond is being prepared to welcome more people to its unique surroundings.

“The whole idea is to make the reservoir more accessible to the community, and we are hoping in the spring — with the partnership of the Parks Department — to open it up for kayaking,” NYC H2O director Matt Molina said.