Minecraft wiki entry for Man-made_lake, associated text: This way works better if you don't actually have a lake yet—in fact if you do, you'll need to fill most of it in with dirt, except for the top layer. (If you don't have a lake or valley at all, you instead dig out the top layer, or at least a 2-block wide outline, 1 block deep.) Go around the edge of your one-block deep depression, and place water in an alternating pattern, like one color of a checkerboard. You should only need to go a couple of squares in—that is, every other space at the edge, and the alternating spaces just inside them—before the water springs multiply to fill your space. If you dug the two-block-outline, at this point you should dig out the interior and let the springs multiply over the whole area. Check for any missing springs and fill them.