Defining swimmable rivers
What is a swimmable river? Is it a river that has a low risk of making swimmers sick? Or is it how pleasant it is to swim in?
A muddy brown river is not attractive for swimming, nor is getting covered in swathes of green algae.
The most widely used definition of what is considered swimmable is based around the risk of getting sick, as defined in the Ministry of Health guidelines.
These guidelines are based on levels of E. coli – a faecal coliform bacteria that can be easily measured and is a good indicator of whether more serious pathogens are present.
These guidelines are broadly described using a traffic light system where green is considered swimmable and red is unsafe for swimming. Green or acceptable has less than 260 units of E. coli per 100ml; amber or alert, 261-550 units; and red or action has 550 units.
To put this into perspective, drinking water standards are a whole lot tougher and require the E. coli count to be less than one unit of E. coli per 100ml.
So how do these Ministry of Health guidelines compare with the recently introduced National Policy Statement on freshwater management? These standards set ‘bottom lines’ for rivers and the recent debate has centred on whether setting wadeable as the bottom line is acceptable.
The standards are divided into bands A,B, C and D.
The bottom line is 1000 E. coli per 100ml or the upper limit of band C, which is described as low risk for wading with an E. coli count between 540 and 1000.
This means that water in B and C is classed as acceptable under the new standards and can be waded in with little risk, but it is not considered safe to swim in without significant risk of illness. And this is the essence of the wadeable versus swimmable debate.
It is likely there will be a further round of consultation about whether this standard is acceptable.
The choice is either to set a low standard and accept that poor quality water is here to stay, or set the bar higher and make swimmable a priority.
Horizons Regional Council signs offer guidelines for safe swimming in local rivers.