Two boats of the same kind make the next boat in the chain:
Merge. Drag a boat onto the same kind of boat, or tap one and then the other. The two become the next, bigger boat.
Move. Drag a boat to open water to move it. A boat can't be dropped on a different kind of boat. Moves and merges both count.
Tide. The dots count down the moves to the next tide. The tide drops the boats shown on the right into open water. It comes every 4 moves, every 3 after 15 tides, and brings more boats as the game goes on.
Driftwood. From the third tide, driftwood washes in. It can't be moved. Merge right next to it to clear it.
Streak. Merge again and again without a plain move in between. Each merge in a row pays more, up to ×3.
Lightship. Two cargo ships make a lightship. It sails out at once, pays 2,500 points and clears all driftwood in its row and column.
End. The game ends when the tide has no room for its boats, or when nothing can merge or move.
Daily harbour. The same tides for everyone today. Your harbour is saved after every move, so Continue picks it up later.
Keyboard: arrow keys move between spaces, Enter or Space picks up and drops, Esc opens the menu.