The pool doesn't have to be empty.
Have you been moving something along with you lately?
Move the fish into the final pod in the pool. You may need to backtrack to either of the previous pods if you haven't been moving the fish as you go. Note: You can also wait to complete this step until you have all the lights set up correctly. This will give you an alternate view of this puzzle's end result.
Now I see what the sunflower is pointing at; how am I supposed to get light on it?