Everybody knows a brook, an at first sight seemingly unimposing living space. Be it a mountain torrent, a shady forest creek or a peacefully meandering stream in a flat land, all these types of brooks have one thing in common: the crowns of the trees along the banks touch each other with their branches. And, in almost all brooks, the dwellers are in retreat. Studies have revealed that in 94% of the flowing waters, the original community of the ancestral animal species does not exist any longer. What had happened? And how will everything go on?