Certainly the incident of infection by any water borne pathogen is basically small. Especially in a remote natural pond. But as Nature would have it, the incident of infection is in direct proportion to the level of human use (immersion). The more people that utilize a body of water for recreational swimming coupled with the level of use (cumulative person/hours)the higher the chances of infection. E coli is a prime example of this relationship. the occurrence of intestinal parasites such as Giardia and Cryptosporidium also relates directly to the frequency (and hygiene) of human use.
