Dive into the ocean

"Let's swim a little first," Yu Dong turned to the two mers who were following after her, she wanted to see how good the two of them were before taking them any deeper in the ocean, lest their legs started to cramp while they were swimming it will be too dangerous. The ocean was calm at the moment but Yu Dong would rather be cautious than let any dangerous situation happen which was why she suggested that they swam first near the shore before going any deeper. 

" You two take a lap around this boulder and then we will see whether we can go any further or not," after she spoke she slowly descended into the ocean. The ocean was very gentle with only ripples on the surface, Yu Dong warned the dangerous sea creatures to stay away from this area while tracing the smaller ones that were far away from here.