...well you're not entirely sure what it's filled with. The consistency is too think to be water, but it's not really firm enough to be considered solid. It's color is difficult to ascertain, but it seems sort of blueish-green. Though whether that's the color of the stuff of the color of the pool interior you couldn't really say.
You stare at the stuff for a bit before picking up a small stone you'd been carrying with you and attempt to skip it across the pool. The rock just sticks to the stuff and sits there on the surface. Not sinking. You realize that you should probably leave this stuff alone. It's clearly nothing you've encountered before, but curiosity gets the better of you and you walk up and touch the stuff with your right-hand index finger. The stuff is warmer then you expected. You press your hand against it and watch it slowly sink in. Pushing your luck a bit you put your hand entirely within the ooze. It a bit like sinking your hand in warm Jello. You decide that since you're curiosity is fulfilled that it's probably high time you high-tailed it out of here. The goo seems to have other idea.