Smithsonian National Zoo biologist Leigh Pitsko carries out a male lion cub for its swim test in a moat in Washington May 6, 2014. Four, unnamed ten-week old lion cubs were tested today for their ability to swim and remove themselves from their zoo habitat moat. (Photo by Gary Cameron/Reuters)

Smithsonian National Zoo biologist Leigh Pitsko releases a male lion cub for its swim test in the zoo habitat moat, in Washington May 6, 2014. (Photo by Gary Cameron/Reuters)

Smithsonian National Zoo biologist Leigh Pitsko releases a male lion cub for its swim test in the zoo habitat moat, in Washington May 6, 2014. (Photo by Gary Cameron/Reuters)

Smithsonian National Zoo animal keeper J.T. Taylor carries out a female lion cub for its swim test in the zoo habiat moat, in Washington May 6, 2014. (Photo by Gary Cameron/Reuters)

Smithsonian National Zoo animal keeper J.T. Taylor releases a female lion cub for its swim test in the zoo habitat moat, in Washington May 6, 2014. (Photo by Gary Cameron/Reuters)

Smithsonian National Zoo animal keeper J.T. Taylor releases a female lion cub for its swim test in the zoo habitat moat, in Washington May 6, 2014. (Photo by Gary Cameron/Reuters)

Smithsonian National Zoo animal keeper Kristen Clark chases a male lion cub during its swim test in the zoo habitat moat, in Washington May 6, 2014. (Photo by Gary Cameron/Reuters)

Smithsonian National Zoo animal keepers J.T. Taylor (R) and Kristen Clark (L) carefully handle a female lion cub after its swim test in the zoo habitat moat in Washington May 6, 2014. (Photo by Gary Cameron/Reuters)

Smithsonian National Zoo animal keeper Marie Magnuson (L) and zoo curator of cats Carig Saffoe (R) are sprayed by a female lion cub after its swim test in the zoo habitat moat, in Washington May 6, 2014. (Photo by Gary Cameron/Reuters)