Pokémon Season 1 Episode 19

Stuck in Porta Vista because they missed the boat, Ash and friends sit around waiting for the next boat and witness a great explosion. They later discover that it is a group of Tentacool that is attacking the city since construction is destroying their reef. Ash and his friends manage to appease the giant Tentacruel and continue on their journey, with Misty catching a Horsea that was being harassed by the Tentacool.