My solution:
Second lemming mines on third stair. First lemming builds over gap at the end of the metal. Third lemming builds back to the OWW on the left. First lemming bashes to stop building (he will have laid just one brick) and builds twice to reach the ledge on the right over the water. Make him a floater at the *bottom* of his fall. He bashes left through OWW, mines at a precise point (I think it's directly beneath the edge of the fourth and fifth metal plates), bashes after four strokes. Build right from the top of the stairs on the left, bash OWW. Crowd go to far left then come back up bridge. Bash through it.
Special_Gunpowder's solution:
Have the third lemming bash through the wooden steps. Make lemming one build over the thin gap and have lemming four close the gap to the left with another bridge. Have the second lemming mine to turn around when he's on top of the OWW and then when he falls down the pit, have him mine and bash his way through the yellow bricks to the left. When he emerges out the other side, have him build (he should be low enough to survive the fall from the end of the bridge). Have lemming one build across to the platform above the water, float down and bash through the OWW (as in part one). Free the group of lemmings by bashing through the bridge and then use the remaining basher to get through the right-pointing OWW.
Conway's solution:
Lem3 bashes through the steps. Lem4 builds to the left to the OWW. Lem1 builds over the narrow gap. Lem2 mines on the OWW, turns to the second narrow gap, and bashes onto the room. Lem1 does the same thing the hero does in Fall and No Life. Lem2 mines out the room to the left, walks up the stairs, and turns. Make him build a step or two back from the very edge of the top step (so his first step can block the path of lemmings walking up), and make him bash through to release the others. Finally bash the remaining OWW.