Cyanobacteria (commonly known as blue-green algae) are photosynthetic prokaryotic organisms that are integral parts of many terrestrial and aquatic ecosystems. In aquatic environments, under favourable conditions, cyanobacterial cells can multiply and form planktonic (suspended in the water column) blooms or dense benthic (attached to the substrate) mats. An increasing number of cyanobacterial species are known to include toxin-producing strains. These natural toxins, known as cyanotoxins, are a threat to humans and animals when consumed in drinking water or by contact during recreational activities. The mechanisms of toxicity for cyanotoxins are very diverse, ranging from acute unspecified intoxication symptoms (eg, rapid onset of nausea and diarrhoea), to gastroenteritis and other specific effects, such as hepatotoxicity (liver damage) and possibly carcinogenesis.
For the purposes of applying these guidelines, contact recreation covers all of those activities that bring people physically in contact with water and involve a risk of involuntary ingestion or inhalation of water. Swimming, whether partially or fully immersed, is perhaps the most obvious one, but others include kayaking, white-water rafting, water skiing, sailing and diving. This definition is consistent with that used for the Microbiological Water Quality Guidelines for Marine and Freshwater Recreational Areas (Ministry for the Environment and Ministry of Health, 2002).
These guidelines are based on the multi-tiered approach recommended by the World Health Organization (WHO, 2003) and the Australian National Health and Medical Research Council (NHMRC, 2008). These organisations recommend that when developing guidelines for cyanobacteria in fresh water, the following should be considered:
The WHO and NHMRC have found that a single guideline value is not appropriate, and both use a series of guideline values associated with incremental severity and probability. The New Zealand guidelines use a similar approach and are based on a three-tier alert-level framework. This framework incorporates a monitoring and management action sequence which regulators can use for a graduated response to the onset and progress of a cyanobacterial bloom or benthic proliferation in the water body. The thresholds can also be applied when responding to an unexpected cyanobacterial bloom event. Two separate frameworks are given: one for planktonic (water column) cyanobacteria and the second for benthic (attached to substrate) cyanobacteria.
A major change in these guidelines (for planktonic cyanobacteria only) from current standard practice is the use of estimates of biovolume as thresholds in the alert-level framework instead of cell concentrations. This is in response to a recent increase in the reported high concentrations of picocyanobacteria (small cyanobacteria, less than 2 µm in diameter) in some New Zealand water bodies. Biovolume takes into account the variability in size between cyanobacterial species and thus allows for a more accurate assessment of health risk.
The health risks associated with benthic cyanobacteria are less well known than the risks for their planktonic counterparts. There has been little international research in this area and no attempts to develop quantitative guidelines. Yet benthic, mat-forming cyanobacteria are widespread throughout New Zealand rivers, and recent investigations have revealed the widespread distribution of toxic species commonly linked to dog poisonings (Wood, Selwood, Rueckert et al, 2007; Heath et al, 2009a, 2009b; Wood, Heath, McGregor et al, 2009; Wood, Heath and Ryan, 2009). Research also indicates the presence of uncharacterised toxins within benthic mats (Wood, unpublished data). In this document, guidelines based on preliminary research are given, but it is anticipated that these will require further refining as knowledge and monitoring tools improve.
These guidelines also suggest that cyanotoxin testing (ie, measuring the concentration of toxin produced by the cyanobacteria in a sample) should be considered as a useful addition to biovolume and mat coverage assessments when surveillance indicates that potentially toxic species are present. Cyanotoxin testing is useful to:
People are generally free to swim or undertake other water-based activities wherever they like in and around New Zealand’s many rivers and lakes, but it would be impossible to monitor them all. Criteria for identifying which areas to monitor will vary from region to region, but will generally be based on the type and frequency of human recreational usage, the available information, and the resources available to the monitoring agency.
In general, blooms are much more common in summer months, and this is when routine monitoring should occur. However, the causes of cyanobacterial blooms are many, varied and often interrelated (see Section 4.6). Blooms and benthic proliferations may undergo rapid changes in extent and toxicity. These complexities mean deciding when and where to monitor can be challenging. Information is provided in Section 4 to assist agencies through a decision-making process for monitoring and sampling.
The New Zealand Ministry for the Environment and the Ministry of Health recommend that the general areas to be included in any routine monitoring programme be agreed by the regional council, territorial authority and public health unit, and documented in a regional protocol. However, in recognition of the monitoring challenges, there will be a need to retain flexibility about sites and the timing of visits.
Determining which agency is responsible for which roles in monitoring and reporting for public health protection needs to be established before developing a sampling and reporting programme. Roles and responsibilities should be agreed for both routine monitoring programmes as well as management responses to bloom events at locations that are not routinely monitored.
Roles and responsibilities are best tailored to suit each region, and decisions will depend on many factors, such as institutional arrangements and available expertise. However, as a general guide the Ministry for the Environment and Ministry of Health recommend the following framework.
The recommended framework below is largely consistent with recommendations for the routine monitoring and reporting of microbiological health risks provided in the Microbiological Water Quality Guidelines for Marine and Freshwater Recreational Areas (Ministry for the Environment and Ministry of Health, 2002).
Occasionally cyanobacterial blooms will occur at locations that are not part of routine monitoring programmes. By default, steps 4 to 9 above could be applied, but the ultimate decision about who takes the lead role may be determined by the extent to which the event is considered a public health risk management issue or a wider resource management issue.
Regional councils, territorial authorities and public health units should clearly identify and agree on a lead agency to develop a monitoring protocol covering both scenarios just described. This protocol should be based on each agency’s respective legislative functions relating to recreational water-quality monitoring and reporting. The protocol should specify details of:
Consideration should also be given to the role of non-regulatory groups, such as community groups and/or iwi. Interactions between communities, authorities and organisations are a key requirement in monitoring, reporting and resolving water-quality issues.
Regional councils and the Ministry for the Environment have responsibilities under the Resource Management Act (RMA) to monitor the state (ie, condition or health) of the environment. Reporting on the state of the environment, and how it is changing over time, is undertaken at both regional and national scales by these agencies. The purpose of state of the environment monitoring and reporting is to measure how well our management practices, policies and laws are working, and whether environmental outcomes are being achieved.
There are many factors relating to human land uses and activities that cause cyanobacterial blooms and mats to form, or that exacerbate naturally occurring blooms and mats (eg, flow alteration, shade reduction, nutrient input). It is therefore important to capture information about bloom occurrence to assist with the interpretation of the impacts of catchment land uses (in addition to managing health risks).
At the time of writing these interim guidelines (2009) there are no national environmental indicators that relate to cyanobacterial bloom and mat events. However, some regional councils report qualitatively on cyanobacterial blooms and mats, and whether cyanotoxins were found. Collating data on the number of sites per region per year where cyanotoxins have been identified, along with the toxin type and algae species, could provide a useful regional and national summary of cyanotoxin occurrence. Once risk thresholds are embedded in regional programmes in a standardised way, it may be possible to begin collating exceedance data on biovolumes, cell counts and toxin concentrations.
As with any monitoring network, caution is needed when drawing conclusions about overall bloom and mat occurrence and risk across New Zealand based on limited sample points.
Undertaking monitoring in accordance with these guidelines has cost and resource implications for the agencies involved. In particular, there are costs associated with increasing the frequency of sampling and/or introducing toxin testing. A number of agencies in New Zealand provide toxin testing services (see Appendix 8) and can provide information to help resource managers assess the feasibility of introducing these services.
Compliance with these guidelines does not guarantee that a water body is safe. Sampling may miss or under-represent a toxic bloom event, or there may be other water-quality problems, such as microbiological, chemical and physical quality, that pose a health risk. It is important that water managers use these guidelines judiciously and consider carefully how they can best be applied.
See Sections 1.2 and 1.3 for more detail on what these guidelines should and should not be used for.