Along the upper Rhine, calico crayfish are stripping entire ponds bare, and researchers find tens of thousands of them crowded into a single pool. Originally from North America, the species reproduces at speeds that let it outcompete native amphibians and dragonflies, and the film tracks how it wrecked a marsh turtle reintroduction project that cost millions of euros. A research team from Karlsruhe studies whether small, isolated biotopes can still be protected even though full eradication is no longer possible, weighing the cost and practicality of intervention. A local fisherman takes matters into his own hands, catching and eating as many crayfish as he can, though the film questions whether that makes any real dent in the population. Interviews with frustrated scientists and fishers sit alongside footage of the crayfish-choked waters themselves, building a case study in how one invasive species can rewrite an entire ecosystem, and what, if anything, can be done once it has already taken hold.