Swimming safety depends largely on the levels of pathogenic organisms in the water. Higher levels of fecal indicator bacteria (FIB) in the water are associated with a greater risk of illness from water-contact recreational activities.
Causes of Recreational Water Pollution
Most beach closings and advisories are the result of monitoring that detects elevated levels of bacteria, which indicate the presence of potentially harmful micro-organisms from human or animal wastes.
These wastes typically enter coastal waters from:
- Runoff from urban, suburban, and rural areas
- Sanitary sewer overflows, line breaks, and spills
- Sewage-treatment plants
Wastes can originate from other sources:
- Malfunctioning septic systems
- Waste from other swimmers, pets and other domestic animals, marine mammals and birds
- Boats
- Improperly disposed dirty diapers
When storms occur in coastal counties, advisories may be issued as a precautionary measure, because heavy rains may cause potentially harmful levels of pollution to beaches, making them unsuitable for swimming and surfing for at least 72 hours.
- The California Microbial Source Identification Manual: A Tiered Approach to Identifying Fecal Pollution Sources to Beaches
This source identification manual provides guidance for cost-effectively identifying sources of fecal contamination within a watershed. The manual is based on a hypothesis-driven and tiered approach, in which the user implements the least expensive options first and more expensive tools only when sufficient uncertainty warrants their use.
Risks of Recreational Water Pollution
Disease-causing organisms, knows as pathogens, may be present at or near the pollutant's point of entry. Gastroenteritis is the most common illness associated with swimming in water polluted by sewage. It occurs in a variety of forms that can have one or more of the following symptoms: nausea, vomiting, stomach ache, diarrhea, headache and fever.
Other minor illnesses that can result from swimming in polluted water include ear, eye, skin, nose, and throat infections. In highly polluted water, swimmers may occasionally be exposed to more serious diseases like dysentery, hepatitis, cholera and typhoid fever.
Swimmers contacting a sewage-borne illness may also pass the disease on to household members. Children, the elderly, and people with weakened immune systems are most likely to develop illnesses or infections after swimming in polluted water. However, swimming-related illnesses are typically minor.
Harmful Algal Blooms Also Pose Risks to Swimming and Other Water Recreation
When conditions are optimal, including light and temperature, levels of nutrients, and lack of water turbulence, cyanobacteria and some algae can quickly multiply into a harmful algal bloom (HAB). Some cyanobacteria and harmful algae can produce toxic chemicals, including cyanotoxins, domoic acid, and other algal toxins that can harm humans and animals that come in contact with the water, with water spray, and or algal matts in the water and along the shore or that consume fish or shellfish from the water.
(updated 8/11/16)
