.. Move the waterfall

Look up the waterfall. You see a symbol. It is the same symbol that is in the empty pool.

There's corresponding symbols on those stone slabs with the four stone switch.

It is important which way the strange symbol is.

By pushing the stones down you denote where the slabs symbols belongs.

For example, the slab with the two circle symbol should be in right. So push down the right stone.

Here's two more

One of the slabs is behind the fallen rocks. Go down to find it.