Wouldn't it be great if we could tell the state of an ecosystem or the like - healthy or heading for a crisis - by keeping track of a few key signals? Thanks to the theory of ‘tipping points’, that’s not unthinkable. Now a team of researchers led by Alena Gsell of the Netherlands Institute of Ecology (NIOO-KNAW) has tested early warning signals: in lakes. In the Early Edition of PNAS online, they conclude that predicting works...but not yet in all cases.