Hamtaro: Ham-Hams Ahoy!(2003)

Tottoko Hamtaro OVA 2: Hamuchanzu no Takara Sagashi Daisaku - Hamuha! Suteki na Umi no Natsuyasumi

As Laura heads out to summer camp, Hamtaro and Oxnard come across a young girl by the name of Haibi, who's trying to find the ocean. Haibi found a treasure map while searching through the storage burrow and is now willing to find the treasure to help her heat exhausted granny. The Ham-Hams, who are more than willing to help her, pack their things and set out to find the treasure.

(Source: Wikipedia)