H2O: Just Add Water (2006)

S3E25 A Date With Destiny

Cleo realizes that a comet is driving fish away from the waters near Mako Island. The girls come up with a plan to reactivate the message in the Moon Pool and learn that the comet is on a collision course with Earth. Meanwhile, Sophie encounters Ryan, and with Zane's assistance, they team up to extract the crystals from the Moon Pool.