Lindsey

Lindsey is a character of the day who appeared in An Undersea Place to Call Home!. She is an underwater archaeologist along with her husband Eddy.

While cruising along the Muraille Coast, the couple stopped to help Ash and his friends after Ash's Pikachu was poisoned by a Skrelp. Lindsey immediately pulled out her first-aid kit and used her Antidote to heal Pikachu. She and Eddy introduced themselves to the group and explained they were going to dive in a specific area in the sea that same day, looking for the remains of the shipwrecked S.S. Cussler that had crashed into an iceberg long ago. Seeing everyone's enthusiasm, the couple allowed the group to join them on their expedition.

Lindsey was later accompanied by Ash and Serena in her submarine. They were quickly swept away by some strong underwater currents, but in the process, they found the remains of the S.S. Cussler. They also discovered Team Rocket was also scouring the ship in search of hidden treasure. Team Rocket managed to escape with the S.S. Cussler's safe, and in doing so, they caused the remains of the sunken ship to flood completely. Lindsey, Ash, and Serena managed to escape in time, and they assisted the Pokémon living around the ship to stop the S.S. Cussler from being destroyed with a metal plate used as a seal. When that plan succeeded, Lindsey was told by Eddy to come back to the surface as the strong currents would appear again soon.

While Lindsey's submarine was not caught up in the whirlpools, Team Rocket was sent blasting off, and the stolen safe sunk back into the ocean. Afterward, Lindsey became particularly impressed with the Water Pokémon that called the S.S. Cussler their home.

(Source: Bulbapedia)