Manga by author Amano Kozue - Status ongoing

Hikari Kohinata is a cheerful 15 year-old girl who lives near the ocean and she spends much of her time diving as a result. On her first day of high school, she meets a teacher who also likes scuba diving. There's also a 16 year-old classmate, Futaba Ooki, who gets dragged along in Hikari's maelstrom as soon as they meet at school.

From ADV Manga:On the planet Aqua, a world once known as Mars, Mizunashi Akari has just made her home in the town of Neo-VENEZIA, a futuristic imitation of the ancient city of Venice. The technology of "Man Home" (formerly Earth) has not entirely reached this planet, and Akari is alone, having no contact with family or friends. Nonetheless, the town, with its charming labyrinths of rivers and canals, becomes Akari's new infatuation, along with the dream of becoming a full-fledged gondolier. Reverting to a more "primitive" lifestyle and pursuing a new trade, the character of Akari becomes both adventurous and heartwarming all at once.

The town of Onobori is located on an island and is protected by a noren (a traditional Japanese curtain). Aka is a naive girl living alone with her grandfather who runs a coffee shop in a quaint windmill hut. An encounter with a giant black cat opens the curtain on a story of creating the colors of the future by weaving together the colorful splendor that is scattered throughout daily life!