Swimming and collecting shellfish is safe in many of New Zealand’s estuaries, beaches, rivers and lakes, but it is important to know when it is not safe, how to recognise signs of water contamination and to be aware of local warnings. This knowledge will minimize the risk of you and your family falling ill from contact with recreational water.
If you swim in or eat shellfish from contaminated water, you risk falling ill
The water quality at more than 80 popular coastal, river and lake recreation sites and shellfish beds in the region are surveyed and monitored by the Bay of Plenty Regional Council from October to March each year. National data is collected from all the local councils and is available on the Land, Air, Water, Aotearoa (LAWA) website. As monitoring only happens in specific places at certain times of the year, it is important for members of the public to know how to recognise signs of water contamination, so that we can keep our community safe together.
Recreational water and shellfish can be contaminated with toxins, viruses and bacteria:
- Toxins are produced by toxic algae (also known as blue-green algae and cyanobacteria), which are naturally found in fresh water lakes and rivers, usually in low concentrations. However, when conditions are favourable, the algae can multiply quickly and form blooms, mats or surface scum.
- Shellfish filter out algae from water as a food source, if the algae are toxic, these toxins can accumulate in the shellfish, making them poisonous to eat.
- Faecal pathogens (such as viruses and bacteria) can contaminate recreational water. Human sewage and animal manure are the main sources of faecal contamination in NZ recreational waters.
Recommendations for safe use of recreational water
1) Do not swim in lakes/rivers/streams/estuaries in the 48 hours after heavy or prolonged rain
Why: Risk of contamination with animal faeces from rural or urban run-off + sewer overflows. Rainfall can wash livestock faecal matter from farmland into waterways.
Potential consequences: Bacterial contamination of water can lead to infections of the gastrointestinal tract (tummy bugs) and skin/eye/ear infections and breathing difficulties.
2) Avoid contact with water if the river bed or rocks are covered in leathery mats of black/brown algae and do not eat shellfish from there
Why: This is a sign of potentially toxic algae
Potential consequences: Toxic algae are capable of producing toxins that are harmful to humans and animals, whether swallowed or exposed to skin. This can lead to fever, headaches, skin rashes, stomach cramps, tingling and numbness around the mouth or face, difficulty swallowing or breathing, dizziness, double vision, and in severe cases paralysis and respiratory failure (can be life threatening).
3) Avoid contact with water that is murky or has a musty smell and do not eat shellfish from there
Why: This is a general sign of contaminated water; it could be toxic algae or bacterial contamination.
Potential consequences: The same as 1) and 2)
4) Avoid swimming near or collecting shellfish where: Pipes/culverts run down to the waterway, sewage or storm water is discharged or there are a lot of houses nearby, farm animals are grazing nearby, there may be industrial pollution, boats may discharge sewage, or near wharves an marinas in general.
Why: These are high risk areas for faecal contamination of the water.
Potential consequences: The same as 1) and 2)
Why: The water quality can fluctuate over time, with temporary warnings being put in place
Potential consequences: It is not always possible to place signage at all parts of a river or lake that may be affected, so it is important to check online, in addition to using your own judgement.
Toxic algae, also known as blue-green algae and cyanobacteria, are capable of producing toxins that are harmful to humans and animals, whether swallowed or exposed to skin during swimming, kayaking or water-skiing. Symptoms include fever, headaches, dizziness, skin rashes, stomach cramps and aggravated hay fever and asthma and damage to the nervous system. People are advised not paddle, wade, swim or participate in any other activity that may involve direct contact with the algae or swallowing of lake water.
Where there is an algal bloom in a lake, it seems unlikely that there is any risk from eating the flesh of trout but it’s very important to remove the gut and liver and wash in clean water first. Do not take or consume trout that are found already dead. Shellfish and kōura (freshwater crayfish) should not be eaten as would likely present a risk to health.
In built up areas such as Tauranga Harbour there is a possibility of sewage discharge from the reticulated sewage system. This can lead to contaminated water. Should this occur, the local authority would advise the public that an unplanned sewer overflow has occurred and remedy the affected area.
For more information about sewer overflows, contact your local council.
Water contaminated with animal and human faeces can lead to gastrointestinal illnesses (tummy bugs) such as Salmonella, Giardia, Campylobacter and Cryptosporidium. People can also experience cold and flu-like symptoms and skin, eye and ear infections.
Swimming, spa and geothermal pools
Swimmers itch, also known as ‘duck itch’ or cercarial dermatitis, is caused by exposure to tiny larvae or cercariae in shallow, warm water and can cause an allergic irritation of the skin.
Symptoms can include an itchy or tingling sensation that develops in to tiny red spots, pimple-like bumps (papules) and occasionally, hives or blisters.
You can reduce the risk of being affected by avoiding shallow areas of water, particularly where there is vegetation and/or evidence of bird life, and washing or showering with clean water following any contact. Drying yourself off with a towel after swimming can also help.
For more information on swimmers itch, see DermNet NZ.
People who get itchy, sore rashes under their swimming costume after swimming at a beach are likely to have been stung by tiny, transparent jellyfish or anemone larvae. The rash is called “seabather’s eruption” and it is the skin’s reaction to the toxin injected by the larvae of jellyfish or anemones.
This rash is often called “sea lice bites”, but sea lice are actually a parasite of fish and they can produce a rash on uncovered skin.
Symptoms of seabather’s eruption include pain, burning and itching. The rash appears as red swollen marks on areas of skin that were covered by swimwear. People can get skin tingling before leaving the sea, and the rash tends to occur after getting out of the water. The rash may not appear until several hours after being in the sea. The rash and itchy can vary from mild to severe lasting up to a week or more. Children and those with a severe reaction can become unwell with headaches, nausea and lethargy for several days.
Warm weather and onshore winds bring tiny jellyfish and anemone larvae close to the shoreline and being so small, they can get trapped unnoticed in swimwear, or in peoples’ hair while swimming. As a swimmer gets out of the sea, water drains from the swimwear and traps the jellyfish between the fabric and the skin, causing the stinging cells to release their toxin. The toxin can also be released by washing in fresh water and rubbing affected skin with a towel.
You can treat the rash by washing the affected area with salt water. Fresh water can be used, but sometimes can make the rash worse. Hydrocortisone cream (1%) applied 2-3 times a day over 1-2 weeks is the most useful treatment. Calamine lotion, antihistamines, and anti-inflammatory medicines such as ibuprofen can also help reduce symptoms. Ask your pharmacist for advice.
If you are concerned or if symptoms are severe see a doctor or call Healthline for advice on 0800 611 116. Healthline operates 24 hours a day, seven days a week.
For more information see DermNet NZ.
- View current local health warnings
- About recreational water quality and health - Environmental Health Indicators New Zealand
- Monitoring information collected by the Bay of Plenty Regional Council and the Waikato Regional Council is available on the Land, Air, Water, Aotearoa (LAWA) website
- Toxic algae blooms - Ministry for Primary Industries
- Advice for Boards of Trustees on maintaining a school pool