This applies to any water where the authorities expect a large number of people to bathe and has not imposed a permanent bathing prohibition, or issued advice against bathing. It is the responsibility of the authorities to identify and assess causes of pollution that might affect bathing waters and impair bathers´ health during the bathing season.The basis for the control of all public used natural swimming ponds is the European Directive "2006/7/EG of the European Parliament, dated 15th February 2006. The Directive has been valid since 24th March 2006.


  • Escherichia coli
  • Enterococci
  • Pseudomonas aeroginosa
  • Legionella pneumophila
  • Cyanobacteria


  • e.g. Cryptosporidian

Chemical and physical characteristics

Dissolved Oxygen

Dissolved oxygen is probably the most critical quality variable in the water. Oxygen levels in pond systems depend on water temperatures, the water salinity, and the amount of aquatic vegetation and animals.


The pH-value is the determination of the hydrogen ion (H+) concentration in water. The pH scale ranges from 0-14 with a pH of 7 being neutral. A pH below 7 is acidic and a pH of above 7 is basic. An optimal pH range is between 6.5 and 8.5, however it should not be lower than pH 5 or above pH 9. pH will vary depending on a number of factors. The pH may rise during the day as phytoplankton and other aquatic plants remove CO2 from the water during photosynthesis. The pH decreases at night because of respiration and production of CO2 by organisms. The fluctuation of pH levels will depend on algae levels as well.


Temperature will affect all chemical and biological processes. Temperature therefore has a direct effect on important factors such as growth and oxygen demand. The higher the temperature, the greater the requirement for oxygen and the faster the growth rate of the plants.


Ammonia is produced from the decomposition of organic wastes resulting in the breakdown of decaying organic matter such as algae and plants. Ammonia levels will depend on the temperature of the water and its pH. For example at a higher temperature and pH, a greater number of ammonium ions are converted into ammonia gas thus causing an increase in toxic ammonia levels within the freshwater.

Nutrient levels

Nutrient levels refer to the amount of phosphorus and nitrogen that are present in the water. Increased levels of nutrients may be harmful. It can cause excessive plankton growth, potential blue-green algae and oxygen depletion.


See article Turbidity