The sixth graders at Stephen A. Halsey Junior High School 157 in Queens have a tough assignment before them: design a new playground that will transform a sea of black asphalt at their school into a recreational oasis — and, while they are at it, help clean up New York City’s waterways.

So, in addition to benches, play equipment, ball courts and drinking fountains, their wish list includes a butterfly garden and a gravel-lined turf field. Those features will capture precipitation and prevent it from overloading the city’s sewer system, which, in the case of their Rego Park neighborhood, spews raw sewage into Flushing Bay when it rains.

In the process, the children are learning about arcane urban infrastructure and bureaucratese, like “combined storm-sewer runoff.” And they are gaining appreciation for the absorbent powers of trees and grass, as well as roof gardens, rain barrels and permeable pavers — bricks that soak up water.

“I always thought the rain ended up in the Atlantic Ocean and that it was cleaned first,” Aryan Bhatt, 11, said.