This paper summarizes the data on the effect of engineered nanoparticles on aquatic organisms. The issues of penetration and accumulation of nanoparticles in the body of hydrobionts and their toxic effect, biotransformation, and migration along food chains are considered. It is demonstrated that the behavior of nanomaterials in the environment and their effect on living organisms have been studied insufficiently and require close attention, because their release into the environment will increase in the very near future.