Monitoring has always been a big challenge both for enforcement of water pollution laws and for understanding the effect of pollution on aquatic ecosystems. Now a group of scientists in the UK may have an answer: robotic fish the size of seals which can swim around on their own, equipped with chemical detectors to sense pollution and wi-fi capability to communicate their data in real time. Plus they look really cool swimming. Of course, there has to be a catch: they cost £ 20,000. It’s not clear whether that figure is per fish or for the group of five that are presently under construction. Either way, though, that’s a pretty expensive monitoring system. Maybe their creators can teach them to reproduce . . .