Red Tide?
Depending on the dive site, there was always a chance of encountering ocean currents while diving.
A downcurrent, as its name implied, was a current flowing downward. The three could tell from the bubbles they exhaled: the bubbles that had been rising suddenly scattered in rings around them, then began drifting downward. The two sea turtles nearby sensed trouble and retreated into a crevice, while the water around the three gradually turned murky.
Fortunately, aside from Zhang Heng, the other two were no novices. Han Lu, included, had encountered currents before and did not panic like beginners would. Standing beside the rock wall, Han Lu immediately pressed herself against it and clung to the surface like a gecko.
Nelly switched on the flashlight she carried and shone it at a large rock closest to Zhang Heng, signaling for him to head over. She swam toward it as well. They were not descending very quickly, which meant the current was not especially strong. That let Nelly breathe a sigh of relief. Han Lu and Zhang Heng were both remarkably composed as well.
The most dangerous thing underwater was panic. Not only did it solve nothing, but struggling wildly accelerated oxygen consumption, and incorrect actions could easily create even bigger problems. Nelly was not too worried about Han Lu, who had plenty of diving experience. What truly concerned her was Zhang Heng, especially since he had just requested to ascend, only for them to encounter a current moments later.
Fortunately, Zhang Heng had not shown any signs of panic so far and swam with Nelly to the large rock.
About a minute and a half later, Nelly felt the current weakening. She gestured to ask Zhang Heng how much air he had left.
Zhang Heng checked his pressure gauge. It