A search for a child in a possible drowning incident was called off Saturday evening at north Minneapolis’ newly opened Webber Natural Swimming Pool after a lifeguard saw two children enter the water from the jumping platform and only one come to the surface.

Authorities later learned that the missing boy had swum to the other end of the pool underwater before emerging for air, scaring the lifeguard and sounding the alarm for emergency protocols.

The pool, which is touted as the only public swimming area in North America to use a natural filtration system, was opened to the public Friday afternoon.

On its opening day, lifeguards assisted at least three youngsters under the age of 12 who were struggling in the pool. But those incidents were not a result of the facility, rather a lack of education by its users, said Dawn Sommers, spokeswoman for the Minneapolis Park and Recreation Board.

“When you have 500 people in [the pool], no matter how trained your lifeguards are, we really need the assistance of parents to be with their kids in that facility — in any facility,” said Sommers, adding that all children under 12 are required to be accompanied by their parents the pool.

Supporters heralded Webber as the first to utilize simulated wetlands, rather than chemicals, to cleanse water. But rain delays, inadequate robotic pool vacuums, unexpected obstacles underground, toad migration and even duck droppings delayed the pool’s opening several times. The project was estimated to cost $7.2 million.