Pokémon : S5 | E48 – Lapras of Luxury

Ash and his friends are returning to New Bark Town, but before Ash is able to get there to register for the Johto League Championship, Professor Elm sends him on an errand to retrieve a Pokémon Egg at the Marine Pokémon Laboratory. At the laboratory, the group meets a young researcher who is in a hurry. As she rushes past them, Brock's heart is sent aflutter and he chases after the woman, with his friends following behind. The researcher rushes to a pier and orders her Lanturn to use Supersonic. The sonar waves echo throughout the water, and the researcher watches intently for any responses. Brock suddenly arrives, but the researcher hushes him so that she can concentrate on her fieldwork. Suddenly the computer picks up the singing voices of traveling Lapras. The Lapras emerge from the water much to the delight of the group and the researcher.

As Ash watches the herd of Lapras from the shore, two adults separate from it, one of which approaches Ash. Ash realizes it's his old buddy, the Lapras that he caught in the Orange Islands, now visibly grown up, and its mother. The researcher is astounded and introduces herself as Naomi, a marine biologist and director of the Marine Laboratory. She reveals that Professor Elm told her that Ash would be coming to retrieve the Pokémon Egg. She takes everyone back to the lab, where she discusses Lapras migration. Naomi says that Lapras's travel routes appear to be linked to water temperature and season. She declares that the key to solving the mystery is in Lapras's voice. Naomi plays the traveling song that Lapras sing when they migrate and explains that her Lanturn's Supersonic can actually pinpoint their location. Meanwhile, Team Rocket spies on the Lapras herd from their Gyarados submarine. James suggests they capture the Lapras and rent them out as water taxi services. Jessie is thrilled with the money-making idea and declares full scheme ahead.
(Source: Bulbapedia)