Lakes and Rivers Summary – 24 January 2008
NEW: Lake Rotoehu Health Warning
Wherever you are swimming be aware that blooms can occur very quickly at this time of year.
If lake or river water looks discoloured, smells, or has scum on the surface or river/lake bed then stay out of the water.
Environment Bay of Plenty regularly tests rivers and lakes for cyanobacteria (blue-green algae).
Exposure to cyanobacteria (the micro-organism that causes the algal bloom) and its toxins can cause severe skin rashes, stomach upsets and aggravate hay fever and asthma.
Lake Rotoehu - Health warning
A health warning was issued for Lake Rotoehu on 24 January, 2008.
“The health warning means people should avoid any activity which results in significant contact with water, says Dr Phil Shoemack, Medical Officer of Health.
Dogs should also avoid swimming in the lake.
Blue green algae have the potential to release toxins which can affect health by aggravating hayfever and asthma, causing skin rashes and damage to the nervous system.
Dr Shoemack says Lake Rotuehu is particularly prone to algal blooms due to its high nutrient loadings and its shallow average depth, which means that sunlight, necessary for algae to grow, can penetrate most of the lake water.
Lake Rotoiti – Health Warning Lifted
Lake users must be cautious at all times. People are advised not to enter the water if it looks discoloured, there is a scum on the surface, or if the water smells unusual.
Kaituna River - Health Warning Lifted
If water looks discoloured, there is a scum on the surface or the water smells unusual - don’t go in.
Lake Rotorua - No health warning
No health warning in place, however, algal blooms have been noticed in the mornings when there is less wind. Use with caution.
Follow this link for an update on the Rotorua Lakes and Kaituna River.
Environment Bay of Plenty has also been monitoring the development of cyanobacteria mats in Eastern Bay of Plenty rivers.
The following is a summary of the status of these mats in the rivers around the Bay of Plenty:
Rangitaiki River - No health warning
The Medical Officer of Health has lifted the health warning advising against recreational use of the Rangitaiki River from Murupara to the river mouth at Thornton.
Whakatane and Waimana Rivers - No health warning
Exercise caution when using the rivers for recreational activity and avoid direct contact with the dark brown/black or golden brown cyanobacterial mats that develop in shallow areas of the river, particularly along the riverbanks. Be aware that these mats can easily become dislodged and move down stream where they can come into contact with swimmers and pets.
Environment Bay of Plenty, district councils, and Toi Te Ora – Public Health will be monitoring the situation. Toi Te Ora - Public Health will update the public when results from further tests are available.
Blue-green algae – How does it affect me?
What are blue-green algae?
Blue-green algae (cyanobacteria) are found in fresh water lakes and rivers throughout the world. They are usually found in small amounts and can only be seen through a microscope. However, when water levels drop and heat up, blue-green algae cells can multiply and form blooms or mats. These can also build up to form surface scum in shallow areas and along the shoreline of lakes and rivers.
What could happen to me if I’m affected by blue-green algae?
Someone who is affected by blue-green algae could have:
- diarrhoea
- vomiting
- abdominal pain
- headaches
- fever
- muscle aches
- achy joints
- dizziness
- flu-like symptoms
- tiredness
- drowsiness
- sore throats
- conjunctivitis (red eyes)
- blistering around the mouth
- itchy skin rashes
- hay fever-like symptoms
- allergic reactions
Hay fever, eczema and dermatitis may also get worse and exposure to blue-green algae may cause an asthma attack.
Blue-green algae can also produce toxins that can damage the liver or poison the nervous system in high doses.
Those at greatest risk of health effects are children and those with pre-existing medical conditions such as long-term liver or kidney disease.
The higher the amount of blue-green algae and its toxins and the longer the contact with the water, the more severe the symptoms are likely to be.
Children can be at greater risk as they might be attracted to play with scum on the shoreline or in shallow areas of a lake or river.
What do blue-green algae look like?
Video of cyanobacteria blooms (16MB, mpg)
Video of cyanobacteria blooms (20MB, mpg)
Please note: These are large files and best viewed from a high speed internet connection.
Blue-green algal blooms will usually make the water a dense blue-green or brown colour.
You might see floating scum when blue-green algae are present in high amounts.
When blue-green algae are present there is usually a musty or earthy smell.
Blue-green algal mats:
- are dark brown/black in colour
- can form in rivers and around lake edges where they usually cover rocks, sand, gravel, logs and weed
- look like moss but have a much slimier texture
- glisten when exposed to air
- can be lighter in colour and look golden brown in shallow areas
- can easily come away from the riverbed and form floating ‘rafts’
Where am I likely to find blue-green algae?
In November 2007, blue-green algal mats were identified in Rangitaiki and Waimana Rivers, and parts of the Whakatane River in the Eastern Bay of Plenty.
You should keep an eye out for any sign of algae in these rivers.
Blue-green algae are widespread throughout New Zealand and could be found in any lake or river – even those with relatively clean looking waters. In the past fifteen years blue-green algae blooms have regularly occurred in several of the Rotorua Lakes, including Lake Rotorua and Rotoiti. They have also been found in the Waikato River and occasionally in the Kaituna River and Lake Taupo.
How am I likely to come into contact with blue-green algae?
People can be exposed to blue-green algae by:
- drinking the affected water
- swallowing the affected water while swimming
- breathing in droplets of the affected water while swimming
- bathing in the affected water
- direct skin contact with the affected water e.g. through paddling, wading, fishing, or launching a boat
The risk is much higher where there are visible signs of blue-green algae blooms, scum collections, or mats.
What happens when blue-green algae is found?
Regional council’s regularly test fresh water (rivers as well as lakes) for blue-green algae. If high amounts of blue-green algae are found, the Medical Officer of Health will issue a health warning. This will advise the public not to drink or use affected water and to keep away from areas affected with blue-green algae.
When a Health Warning is issued, the District Council puts signs up at places where public access the river or lake.
It’s not always possible to put signs all the way along a river or lake that may be affected. You should look out for blue-green algae and avoid using any areas that have visible blue-green algae. Don’t swim if you think it’s there.
You should not paddle, wade, swim, fish, or do anything that might involve contact with blue-green algae. Keep your pets and livestock out of areas affected by blue-green algae.
Anyone suffering illness after contact with blue-green algae blooms should seek medical assistance. Any illness in pets or livestock after contact with affected water should be reported to the Medical Officer of Health.
How can I get up-to-date information on blue-green algae?
Current health warnings are posted on the following websites:
Who should I contact?
I think I have found blue-green algae
- Environment Bay of Plenty - 0800 ENV BOP (368 267)
- Pollution Hotline - 0800 73 83 93 (after hours)
- Environment Waikato (07) 378 6539 (Taupo office)
- Pollution Hotline 0800 800 401(after hours)
I think I’m sick or my child is sick from contact with affected water
If you or your child become sick and think it may be from contact with affected water, you should contact your family doctor immediately.
If you have any concerns, you can contact a Health Protection Officer at Toi Te Ora - Public Health for queries relating to human health and drinking water. Their contact details are:
- Toll free - 0800 221 555
- Tauranga - 07 571 8975
- Rotorua - 07 349 3520
- Whakatane - 07 306 0847
I think my pets/livestock are sick from contact with affected water
If you are concerned about your animals, you should contact a vet immediately. You or your vet should then contact your local council to report any illness resulting from contact with the blue-green algae.
What do I do if my water supply comes from a stream, river or lake affected by blue-green algae?
Boiling the water is not recommended as boiling will cause the blue-green algae cells to break open and will actually increase the toxic levels.
Check the water upstream of your intake and at your intake for the presence of blue-green algae. If you think the water is affected by blue-green algae, contact:
- your local council
- Toi Te Ora - Public Health.
If your water is affected, close off your intake and find an alternative water supply.
Reticulated town supply water is monitored and adequately treated.
Can I water my garden with water affected with blue-green algae?
Yes. Fruit and vegetables do not appear to absorb the toxins. However, fruit and vegetables should be washed in clean water as the blue-green algae may form a residue on the surface, which can remain toxic even when dry.
What is being done to get rid of blue-green algae?
There is little that can be done immediately to get rid of the blue-green algae mats. Environment Bay of Plenty is looking into the ways the land is being used in affected areas to see if anything can be done to reduce nutrient inputs to streams and rivers.
Local councils and Toi Te Ora - Public Health are responsible for issuing health warnings and making sure that the public are aware of the potential risks of blue-green algae.
Where can I get more information on the effects of blue-green algae?
Websites:
Or call:
Toi Te Ora - Public Health for queries relating to human health and drinking water. Call:
- Toll free - 0800 221 555
- Tauranga - 07 571 8975
- Rotorua - 07 349 3520
- Whakatane - 07 306 0847
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