A thermocline is a transition layer between two layers of water. In Barracuda Lake, one layer is sweet and cold, and the other is salty and warm. While diving in Barracuda Lake you will experience many of these thermo clines, most of them are horizontal, but some of them are vertical. You see how the diver on the left hand side is blurry, while the diver on the right hand side is clear? These are the two different layers of water.
If you watch my video, you will be able to see these thermo clines in detail.
Another exceptional dive in Coron is the Cathedral Cave, under Coron Island.