Ryuuguuchou wa Umi no Soko

Ryuuguu is a small town under the sea. Aside from the fact that everything is underwater, it's just like every other small town. Classmates Masora and Sumire are like every other middle school girl, swapping love stories and hanging out at shopping malls. However, Masora is unsettled by the strict control that the town has over information, so she begins to investigate on her own...

(Source: Wani Books, translated)