Glossary of Terms

A long-term water quality classification calculated using results from the most recent 12-month period.

The value below which 90% of the sample results fall. This is used for the Sufficient and Poor classification threshold.

The value below which 95% of the sample results fall. This is used for the Excellent and Good classification thresholds.

A rapid growth of algae or microscopic organisms in water. Some blooms can discolour the water or produce foam or smells, and may be mistaken for pollution.

Always swim where and when lifeguards are on duty, swim between the red and yellow flags, follow lifeguards' instructions, keep children under constant supervision, never swim alone, avoid alcohol, and report hazardous conditions or incidents to lifeguards or beach staff.

A City awareness message encouraging residents to put waste in the bin instead of flushing or pouring it down toilets, sinks, drains or stormwater systems. Items such as wet wipes, nappies, fats, oils, grease, rags and other solid waste can block sewer pipes and drains, causing overflows that may pollute rivers, stormwater systems and coastal waters.

An international beach programme with water quality, education and beach management criteria. Blue Flag water quality sampling is conducted independently during the Blue Flag season. The accreditation, which includes an international adjudication process, is facilitated by the Wildlife and Environment Society of South Africa (WESSA).

The land area that drains into a river, stormwater system, wetland, estuary or coastal area. Activities in the catchment can affect coastal water quality.

"Colony-forming units per 100 millilitres." This is the unit used to report the number of bacteria counted in a water sample.

The documented process used to track samples from collection at the site to laboratory analysis, helping ensure that samples are handled correctly.

A sampling site near a known or potential pollution source, such as a stormwater outlet, river mouth or discharge point. These sites help monitor pollution sources and are not known recreational sites.

A measure of the condition of seawater at coastal sites, especially in relation to possible pollution and recreational use.

Keeping samples cold from collection until they reach the laboratory to help preserve sample quality.

The percentage of samples that were below the selected threshold over a given period. For example, 95% compliance means 95% of samples were within the threshold.

Higher-frequency sampling undertaken for research programmes at selected sites to better understand short-term water quality patterns.

A bloom of microscopic algae called diatoms. Some surf-zone diatom blooms can turn water brown but are not necessarily toxic or unsafe for swimming. This is commonly seen in False Bay's coastal waters.

A type of bacteria commonly found in the intestines of humans and animals. It can indicate faecal contamination, but enterococci is the international best practice indicator for marine recreational waters.

Bacteria used as an indicator of faecal pollution in coastal waters. Higher numbers may indicate a greater chance that other harmful bacteria could be present. The City uses enterococci as the main indicator for coastal recreational water quality as per international best practice (WHO, 2021).

A sample result that is above the selected threshold.

The highest water quality classification. Based on the South African recreational water quality guideline values, this means the 95th percentile is below 100 cfu/100 ml for enterococci and is associated with an estimated less than 2.9% gastrointestinal illness risk per exposure. This is low risk, but not 'no risk'.

Bacteria used to indicate whether water may have been contaminated by human or animal faecal matter. They do not always cause illness themselves, but they help indicate possible health risk.

A longer-term water quality classification calculated using results from the previous five years. This gives a more accurate and holistic picture of water quality trends at a specific site.

A water quality classification indicating relatively low health risk. It means the 95th percentile is below 200 cfu/100 ml for enterococci and is associated with an estimated less than 5% gastrointestinal illness risk per exposure.

A statistical method used to rank sample results and calculate the 90th and 95th percentiles. The City uses this method to assign water quality classifications.

A public notice or warning issued where there may be increased health risk. Health advisories, signage and media releases are issued by City Health.

The classification assigned to a site based on enterococci results over a five-year rolling period and 365-day rolling period. The categories are Excellent, Good, Sufficient and Poor as prescribed by National Guidelines. These categories indicate estimated gastrointestinal illness risk for recreational water use, but importantly: these do not indicate there is 'no risk'.

Large seaweed commonly found along Cape Town's coastline. Decomposing kelp can create odours, foam, dark water or discolouration that may be mistaken for sewage.

The testing of coastal water samples by an accredited laboratory to determine the number of indicator bacteria present.

The actual laboratory result for the most recent sample taken at a specific site.

The status or advisory shown for a beach (Green, Amber Alert or Red Alert), based on the most recent sampling result and aligned to National Guideline operational protocol.

A trained and qualified person or team stationed at selected beaches to help keep beach users safe. Lifeguards monitor designated bathing areas, assist swimmers in difficulty, provide first aid where needed, and advise the public on safe beach use. In Cape Town, lifeguards are stationed at popular beaches during the summer season, generally between 10:00 and 18:00.

A long-term (365-day) classification that flags an ongoing water quality concern at a beach, based on the rolling 12-month category rather than a single sample result.

A coastal wastewater disposal infrastructure that conveys screened or partially treated effluent (wastewater) via offshore pipelines for discharge into the marine environment, where dilution and dispersion occur under regulated environmental conditions applicable to Cape Town's coastal and marine environment.

A pale or milky-looking area in the nearshore water. The milky plume sometimes seen near Camps Bay is not proven to be sewage and is likely linked to calcium carbonate from beach sand sediment.

The coastal water area close to the shore, where swimmers, surfers and beach users are most likely to be recreating.

A way of showing where a value sits in a ranked set of results. For example, the 95th percentile is the value below which 95% of results fall.

A classification indicating that the site did not meet the guideline thresholds for Excellent, Good or Sufficient. It means the 90th percentile is above 185 cfu/100 ml for enterococci and is associated with an estimated greater than 8,5% gastrointestinal illness risk per exposure. A poor classification does not necessarily mean the water is always unsafe; it may reflect occasional elevated results or contamination spikes at a specific site at the time when the sample was taken.

The potential chance of illness from exposure to contaminated water. In coastal water quality, this is mainly linked to the possible presence of faecal contamination and pathogens.

A beach, tidal pool or coastal site used by the public for swimming, surfing or other water-based recreation. These sites are assessed for recreational health risk.

A moving time window, in this case the previous 12 months or previous five years, that updates as new data is added and older data falls out of the calculation.

Scheduled sampling undertaken as part of the City's regular coastal water quality monitoring programme.

Water that flows over land surfaces after rainfall or irrigation and may carry pollutants into rivers, stormwater systems and coastal waters.

A bottle of seawater collected approximately 30cm below the ocean's surface from a specific site and sent to a laboratory for testing.

How often samples are collected at a site, for example weekly or twice a month.

The standard laboratory method used for testing enterococci in coastal water samples.

A report logged with the City of Cape Town when something needs attention, such as pollution, damaged infrastructure, illegal dumping or a sewer overflow. The request is given a reference number so it can be tracked and followed up by the relevant City department.

Wastewater from toilets that contains human waste, including faeces, urine, toilet paper and flush water. Sewage may contain faecal bacteria and pathogens and must be conveyed through the sewer system for treatment.

A release of sewage or wastewater into the environment, often from a broken sewer line, blocked pipe, failed pump station or overflow.

Infrastructure that pumps wastewater from low-lying areas towards a wastewater treatment works. If a pump station fails, wastewater can overflow into the environment.

Rainwater runoff that flows from roads, roofs and hard surfaces into stormwater drains, rivers and the sea. It can carry contaminants, especially after rainfall.

The minimum acceptable classification for recreational use under the National Guidelines for Recreational Use. It means the 90th percentile is below 185 cfu/100 ml for enterococci and is associated with an estimated less than 8.5% gastrointestinal illness risk per exposure.

A classification calculated using summer-period results only (1 October to 31 March) when there is little rainfall. This shows what water quality looks like during the summer months when it is drier and more people tend to visit the beaches.

"Too few data." This means there were not enough samples available to calculate a reliable classification.

A guideline value used to help assess whether a result is elevated. On the dashboard, a single sample above 240 cfu/100 ml is shown as an exceedance of the National Guidelines for Recreational Use.

Used water from homes, businesses, industry and other activities. It includes sewage, as well as water from showers, basins, dishwashing, laundry, cleaning, commercial and industrial processes. Wastewater is conveyed through the sewer system to wastewater treatment works for treatment.

A municipal facility that receives sewage and used water (wastewater) from homes, businesses, industries, and stormwater infiltration, and treats it to an acceptable standard before releasing the treated effluent back into the environment or reusing it.

A classification calculated using winter-period results only. This is useful because rainfall and stormwater runoff can affect coastal water quality in Cape Town, as is the case at all coastal cities around the world.