Beach Health & Water Quality

Harmful Micro-organism Sources

How do harmful Micro-organisms get into the water?

Any transport that helps to carry sewage and wastes to lakes contributes to pollution problems with pathogens. Sewage treatment plant effluent, for example, is often directly disposed of in rivers or streams. Storm sewers carry dog and cat feces off sidewalks and city streets and into streams. Improperly sited or maintained septic systems may discharge pathogens to underlying groundwater. In numerous locations, pipes dispose raw sewage into the lakes. Cattle and other domesticated animals can void feces directly in streams or lakes, as do wild animals and birds. Manure can contribute pathogens to surface water via runoff and erosion.

Once deposited in water and sediments, certain pathogens can persist for periods of several weeks to months. Occasionally, high bacteria counts after a storm are due to resuspended fecal coliforms in sediment rather than to more bacteria entering the water.

Storm water is a major contributor of non-point source pollution in watersheds. E. coli levels in urban storm water have been detected to reach as high as 100,000 CFU/100 ml.

Human fecal pollution in urban areas

is largely attributed to sewage overflows. There are two types of sewage overflows; sanitary sewer overflows (SSOs), and combined sewer overflows (CSOs). SSOs are the release of untreated sewage from municipal sanitary sewers directly into surface water bodies. There are numerous causes of SSOs including extreme weather, system failure, incorrect system operation and maintenance, and vandalism.

Combined sewer systems

carry both sanitary sewage and stormwater. During wet-weather periods these combined systems may exceed capacity due to the increased amount of stormwater in the system and as a result, this combined sewage is discharged directly into the nearby surface waters. E. coli levels have been found to reach 500,000 CFU/100 ml in SSO discharge and 250,000 CFU/100 ml in CSO discharge.

Localized inputs of fecal bacteria from wildlife,

such as waterfowl roosting on shorelines, can negatively impact water quality. According to a study conducted at our laboratory it was found that gulls largely contributed to high E. coli levels, greater than 27,000 CFU/100 ml, at a bird roosting site adjacent to a local beach.


Fecal contamination from agricultural runoff

poses an additional threat to water quality. E. coli levels from rural runoff have been found at times to reach levels of 10,000 to 100,000 CFU/100 ml.


Combined Sewer Overflows (CSO's) are the largest contributor of bacteria and viruses. CSO's combine residential, commercial and industrial wastes which carries pollutants in the form of sewage solids, metals, oil, grease and bacteria. During periods of heavy rain, the water in the CSO's combine with the storm water running over the land. The CSO then becomes overwhelmed with water which forces it to discharge untreated or partially treated wastewater into urban streams, tributaries and into the lakes through the combined sewer overflow. Each year, billions of gallons of untreated sewage from combined sewer outflows are released into the lakes.