Four African lion cubs passed their first swim test Tuesday at the Smithsonian’s National Zoo — a move that puts them a step closer to making their public debut.

The three males and one female, now 10 weeks old, kept their heads above water, navigated to the shallow end of the moat and climbed onto dry land, zoo officials said.

The cubs were born March 2 to 9-year-old lioness Shera. Zoo officials said the “swim reliability test” is an important milestone for the cubs.

“It’s possible that a cub could be playing around and get knocked into the moat by a parent or sibling,” said Kristen Clark, an animal keeper at the Great Cats exhibit. “We want to make sure that if they find themselves in that situation, they know how to pull themselves out of the water and onto shore.”

Clark herself was in the water helping to guide the cubs to stay in the 2 1/2-foot-deep shallow area of the moat and out of the deeper, 9-foot end of the moat that is closest to the public viewing area.

The Smithsonian's National Zoo's four African lion cubs took a swim test Tuesday. The cubs must prove that they can swim to land and pull themselves out of the water before going on exhibit. All of the cubs passed. (Zoeann Murphy/The Washington Post)

Zoo officials said they wanted to keep the cubs toward the shallow end because that’s “where they can actually get out of the water.” There’s no ledge for them to climb out of the moat in the deeper end, according to zoo spokeswoman Jen Zoon.

The four cubs are scheduled to go on view to the public in mid-June after they’ve received all their vaccinations.

Two other lion cubs at the zoo were born to mother Naba on Jan. 24. The two 15-week-old cubs passed their swim test in April will make their public debut Friday. Zookeepers will decide on a day-to-day basis how much time Naba’s two cubs will spend in the yard, depending on the weather and how they adjust to being outdoors.

Luke, the zoo’s 8-year-old male, sired all six cubs.

Zoo officials said they are hoping to have all the lion cubs named by Father’s Day, and they eventually plan to have all nine lions share the same space this summer.