There’s something in the water on Long Island. 

Lifelong friends and brainiac All-American distance swimmers Johnny Macko and Sasha Karafin are making a huge splash in the Bellmore-Merrick school district as super seniors who will dive headfirst into Ivy League pools next year. 

“We’ve always just been on the pool deck together,” Brown University-bound Macko, who was recently named Mepham High School’s salutatorian with a 101.82 GPA, told The Post. 

“We’re always cheering before our races — high-fives, ‘good jobs.’ It’s the little things that matter.” 

Soon-to-be Yale Bulldog Karafin, who has a 100.9 GPA at neighboring John F. Kennedy High School — where the top two academic 12th graders have yet to be announced — added: “I feel like we’re also ultra competitive sometimes.” 

Karafin playfully splashed Macko for earning a 99 on the U.S. History Regents — a final exam on which she scored one point higher. 

“We’re both very proud. We’re both where we want to be,” Macko added. 

Stroke of genius 

The unsinkable duo has thrived on the same club team, Long Island Aquatic, for years. 

Swimming officials adore the 17-year-old role models for their shared attitude and work ethic, which often leads to supportive teachers sitting in the stands to cheer them on. 

Macko and Karafin train intensely together every day and usually practice up to nine times a week for long-yardage events between their club and school squads, which Karafin said has her feeling ready for next year in New Haven. 

“I’m not too nervous,” she added. “I think that we both are going to schools that are very good fits for us, and I’m just excited to get started.” 

Meanwhile, the Macko shark won state titles in both the 200-yard and 500-yard freestyle events, and his 4:28.31 time in the latter earned him All-American honors. 

He feels like swimming and school flow together. 

“It’s almost like a direct relationship,” Macko said. “When one goes up, the other goes up.” 

Karafin added that treading water academically and athletically — while still impressively getting eight hours of sleep — taught her essential time-management skills she’ll bring to college. 

“When I’m at practice, I want to be all in at practice,” she said. “I don’t really want to be thinking about anything else, and I feel like I could say the same for school. I kind of want to have my head in one place.” 

Swim cap and gown 

Once the upcoming county and state championships wrap up, Karafin and Macko will turn their attention to their futures and applaudable aspirations. 

“I think I’m double-majoring in economics and political science,” Karafin said. 

“I want to major in pre-med,” added Macko. 

They’ll still see plenty of each other at Ivy League meets, where there’ll likely be a little light teasing over grades again. 

“The academics, we already work very hard, so hopefully it’s not too much harder,” Macko said. 

“It’s definitely helpful to have people that are high-achieving around you all the time,” Karafin added.