By the first scrimmage at Bushwick, there were seven swimmers, and then 12 by the first meet. Though the season was a losing one, Ms. Taylor finally fielded two dozen mostly competitive swimmers.

“We’re fast learners around here,” said Kyara Rosello, 17, a junior who was a standout in the 100-yard freestyle. Standing on the pool deck recently, she pulled over Jeniffer Montachana, 16, who recently immigrated from Ecuador. Jeniffer has yet to learn English, but she had picked up enough swimming technique within weeks to become one of the team’s starting backstrokers. The girls on her team who spoke no English relied on other students to translate into Spanish.

If the girls wanted to compete further, Ms. Taylor told them of a local swim team whose fee started at $1,000, but none of the girls could afford it.

It was not easy to get students interested in the new swim team.

“Some of our own students didn’t even know we had a pool here,” said Jorge Sandoval, the principal at one of the Bushwick campus schools, the Academy of Urban Planning and Engineering.

So Mr. Carbajal used a financial incentive. He guaranteed nonswimmers that he could have them swimming well enough to pass the city’s preliminary lifeguard test, offered every winter. That could mean spending summers in the sun making at least $16 an hour, he said, and also helping with the city’s notorious lifeguard shortage.

He persuaded more than a dozen boys to join — 80 percent of them nonswimmers, he said. Mr. Carbajal had to buy some of them bathing suits with his own money.

So far the team has won four meets and lost two. It has a slightly ragtag quality, but it is improving quickly. Though it is currently in the least competitive of Brooklyn’s three boys divisions, Mr. Carbajal vowed that the Tigers would finish first and eventually get a chance to challenge perennial swimming powerhouses at elite public high schools like Brooklyn Tech.