ENTER to skip scene.
U to undo.
You need to pollute all lakes. Black rectangle is your factory (source of pollution), dimmed rectangles are pollute.
There is a big network of pipes (black lines if polluted otherwise green lines) which carry your waste.
You need to set direction of pipes so you can pollute all lakes.
You can't choose all directions always, each pipe on node has different pipes it can lead to.
By selecting beginning and end of pipe you can see where it leads. I know that explanation is bad so I included pictures on how to play game.