I have a slanting step; the ground under the step has washed away (underground stream). Here is a photo of the step when it was new.
The general direction of the stream under the deck is from left to right (diagonally). You could use your mouse and go from the bottom left to the Top right and that would tell you the direction of the stream. There was at one time 5 foot of clay just under our top soil and that was a solid foundation ,enough to hold up just about anything. Since 1980 that 5 foot layer of clay has eroded away in some places.
Cleaned the pool yesterday and this morning I checked the pool and it is getting closer to normal; 66 degrees and very clear; I will clean it again today and recheck it this afternoon.