take the water image and use the curves tool and make the image darker. then set the layer to multiply and copy it few times and merg the layers
step 2 of 3
then copy the layer we just made and set the layer to overlay. then use the color balance and chanel mixer.
step 3 of 3
add the layers to the pool image. then make copies of the lava and use a soft brush and erase to blend. then erase to fit the shape of the pool. then add the splash image. use the color range and flick the white of the image. hide the layer and go to the lava layer and use the clone stamp to add the lava splash