There are many reasons for beaches being contaminated. "Fecal contamination occurs due to improperly constructed and operated septic systems and sewage treatment plants, manure spills, storm water runoff from lands with wildlife and pet droppings, or direct contamination from waterfowl, livestock, or small children in the water" (Iowa Department of Natural Resources). Other reasons are the presence of pathogens in the intestines of warm-blooded animals including human beings.
The best way to identify fecal contamination is to use indicator bacteria. Escherichia coli or E. coli and Enterococcus sp. are the indicators used by the Environmental Protection Agency (EPA) office to identify fecal contamination in seas, lakes, ricers, etc.
The indicator bacteria, which are used to identify fecal contamination don't make anyone sick. They are found everywhere in the environment. Presence in high levels of these indicators indicates that has come into contact with fecal material and pathogens or disease causing organisms may be present. Diseases like Diarrhea may be the result when anyone comes in contact with the contaminated water. Illnesses like sore throat, vomiting, sinus infections, stomachache, fever, headache and other skin related diseases might be caused due to the fecal contamination.
One of the difficult tasks for every health organization is to monitoring the beaches.