Grand Blueぐらんぶる; Guran Buru

From MangaHelpers: A new life begins for Kitahara Iori as he begins his college career near the ocean in Izu city, full of excitement for his new life. He will be moving into his Uncle's diving store "Grand Blue." There he finds the beautiful ocean, beautiful women, and men that love diving and alcohol. Will Iori be able to live his dream college life? This manga centers on the budding youthful drama of a college student living along in a coastal city who meets a scuba-diving and fun-loving upperclassmen.