CREEK
Join the channels and the water runs.
Tap a stone to turn it a quarter. When every channel joins, the water runs from the spring through all of them to the lake. Stones with pins in the corners do not turn.
Difficulty
The slider goes from a 4 by 4 creek to a 9 by 9 one. Higher settings pin more stones in place, and the top four settings add stones that carry two channels. Each creek is checked by search, and the note under the board says whether it has exactly one answer.
Credit
Turning tiles to join a network is an old and well-loved loop: Pipe Mania, NetWalk, Simon Tatham's Net, Infinity Loop, Loops of Zen. Nothing you do is sent anywhere, and there are no accounts, ads or tracking.