A mountain spirit is strangely attracted to the club members of the Roman club in the high school near her shrine … and thus begins all their adventures into the unknown.

Invaders from an unknown dimension prey on the loneliness of the human soul. The only thing between them and the success of their diabolical plan is 4 youngsters with powers to rival the invaders!

From Tokyopop:

After 150 years of terraforming, Aqua, the planet formerly known as Mars, now has over 90% of its surface covered by water. A young girl named Akari Mizunashi arrives at the city of Neo-Venezia, an exact replica of the old Italian city of Venice, hoping to become an Undine, the most coveted job on Aqua. Follow Akari's adventures as she discovers the wonders of Aria in this prequel to the popular Aria anime and manga series.

Ohisama Egao collects the stories of the budding romances of three schoolgirls and one teacher - Aoi, Ryouko, Shizu, and Awada-Sensei - and also shows how their lives intersect at school, a small cafe, and elsewhere. Things don't always go smoothly with the schoolboys they like, but like the sunflowers that surround them, the girls keep looking for the sun.

- polm23

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.

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.