The water factor in transfer of the activators toxocariasis was not taken into account by parasitologists earlier. Yet in the urbanized ecosystems (first of all--in the megalopolis) it can have rather appreciable importance in distribution of toxocariasis in animals and man. Our researches which have been carried out in reservoirs of Moscow with the "wild" and the "organized" beaches, have revealed various, but as a whole their significant, of contaminations by invasion eggs Toxocara (Toxocara canis, T. mistax, and Toxascaris leonina). It specifies an opportunity of their hit in organism of the man and, as a consequence--toxocariasis. The examination of the patients toxocariasis of the people (first of all of children at the age of 3-10 years) have confirmed the fact of their bathing and involuntary swallow of water in urban unflowing reservoirs. In ecosystems of the megalopolis at a high level of parasite of pollution increased superinvasion of dogs and cats and free access of animals to internal reservoirs--the risk of infection of the people toxocariasis gradually grows.