Factsheet: Faecal Indicators

What are faecal indicator bacteria?

Faecal indicator bacteria (FIB) are bacteria that come from the gut of warm-blooded animals (including people) and birds.  FIBs are introduced to the environment through faeces ('poos'), and the presence of them in our waterways indicates that other harmful pathogens may also be present.

Some faecal bacteria or pathogens can cause disease in people if they come in contact with them. Pathogens can also accumulate in some types of shellfish, posing a risk to people if eaten.

This is why faecal contamination in water is monitored using FIBs.   The two most commonly measured faecal indicator bacteria are E. coli (in freshwater) and Enterococci (in marine waters).

E. coli

What is E. coli?

E. coli (Escherichia coli ) is a type of bacteria commonly found in the guts of warm-blooded mammals (including people) and birds. High E. coli concentrations in freshwater can be harmful to humans.

Common sources of E. coli bacteria are untreated human wastewater discharges, stormwater run-off and animal waste.  E. coli survives outside the body and can survive for up to four to six weeks in fresh water making it a useful indicator of faecal presence and therefore of disease causing organisms in a river or lake.  Faecal concentrations are typically higher in pastoral streams but even near-pristine streams are not totally free from E. coli because of faecal deposition by birds and wild animals.

Why is too much E. coli a problem?

Too much E. coli means that the water is unsafe to drink or swim in and can cause gastroenteritis, or infections of ears, eyes, nasal cavity, skin, and the upper respiratory tract. Water is only considered safe for drinking if there are very low concentrations of E. coli present. When E. coli in rivers and lakes are detected above 550 per 100 mL, health authorities put up signs warning that swimming or collecting shellfish is not recommended. When E. coli concentrations are high, other faecal pathogens can also be present and might cause illness.

How to test for E. coli?

Water samples are collected by your regional, unitary or local council as part of their State of the Environment or recreational monitoring and sent to laboratories to be tested for E. coli using nationally or internationally approved methods. During the summer months (around November – March), councils collect E. coli weekly at sites where people swim, and these results are shown in the 'Can I Swim Here?' section on LAWA.  

Which unit is it given in?

E. coli can be counted under the microscope as Colony Forming Units (cfu) or Most Probable Number (MPN) per 100 mL.



What are enterococci?

Enterococci are bacteria that naturally occur in the gut of humans and animals as well as birds, fish and reptiles. These are the preferred biological indicator for faecal contamination of coastal swimming sites. Enterococci are the bacterial indicator for marine water.

How to test for enterococci?

Water samples are collected weekly from popular swimming sites by regional, unitary or local councils during the swimming season (usually November – March), and these results are shown in the 'Can I Swim Here?' section on LAWA.

Which unit is it given in?

Enterococci are counted under the microscope as Colony Forming Units (cfu) per 100 mL.


Why not monitor for pathogens?

At the moment, monitoring directly for pathogens is cost prohibitive.  The number of pathogens that would need to be tested, and the difficulty in testing these in the laboratory means that we use indicators, FIBs, to let us know if faecal material is present in the water.  We know when levels of FIBs may start to cause illness in people using the water, which makes them a robust, reliable indicator.

 Why is there a delay in getting FIB results?

Water samples are collected and then sent to the laboratory.  At the lab a sample of water is put onto a special substance (selective media) which encourages the growth of any FIB present in the sample.  After 24 hours, any FIB organisms present will have formed a colony, which are counted.  This is why there is a delay in taking a water sample and obtaining a water quality result.

Where do I find more information?

Microbial Water Quality Guidelines for Marine and Freshwater Recreational Areas (2003). New Zealand Ministry for Environment and Ministry of Health.