Black Water: Abyss (2020) on Netflix

Plot summary

Five friends travel into a forest in northern Australia to see a cave that Cash has located. Eric, Jennifer, Yolanda and Viktor follow him down to an underground lake, brushing off the storm warning on his phone. Rain sets in above them and the passage they came through vanishes under the rising water. Viktor spots something in the lake, goes after it and comes back badly hurt. With the only known way out flooded and the air running thin, the friends split up to hunt for another passage to the surface, and something is moving in the water beneath them.