Comment: E coli monitoring tells us that bugs are in the water, but not where they came from. For that we need "faecal source tracking" tools to find out "whodunit", writes Federated Farmers Senior Policy Adviser Elizabeth McGruddy.

The swimming season is upon us. Are our favourite swimming spots good to go? And if not, why not?

We know that most rivers are safe to swim, but some are not. Currently around 70 per cent of swimmable rivers (rivers with enough water to get wet in) are safe for primary contact. The national target is 80 per cent by 2030, and 90 per cent by 2040.

The Government's latest freshwater proposals recommend that priority be given to the popular swimming rivers, during the swimming season.


Regional Councils are expected to monitor these sites every week through summer to check for presence of E. coli (bacteria found in faeces).

If any sites breach the swimming standards, the next step is to identify the causes and develop Action Plans to address them. Federated Farmers agree this a sensible priority and a sensible plan.

Federated Farmers Senior Policy Adviser Elizabeth McGruddy. Photo / Supplied
Federated Farmers Senior Policy Adviser Elizabeth McGruddy. Photo / Supplied

E coli monitoring can tell us that bugs are in the water, but it won't tell us where they came from. For that we need "faecal source tracking" tools to find out "whodunit" – was it humans or animals or maybe ducks?

In November Environment Southland released the results of work by ESR analysing "whodunit" from 50 sites across Southland.

The smallest source was human (detected at ten of the 50 sites). But because human bugs are "host specific", human waste is considered the greatest risk to human health. ESR recommend first priority to keeping human waste out of water.

At base flow (when it's not raining), the dominant source across all catchments was wildfowl, presumably from direct deposition (into or adjacent to the water).

After rain, the dominant source was ruminant (cow, sheep, deer, goat), presumably from run-off.

The levels were highly variable: at some sites ruminants were estimated as less than 1 per cent of the load, at others up to 100 per cent.


Levels from ruminants seemed to peak around autumn, suggesting autumn rains flushing accumulated material off the paddock.

ESR suggested a range of strategies – first priority to fixing any failing sewerage networks or septic tanks, looking at strategic places to intercept runoff, culling wildfowl – but their major recommendation was that one-size solutions would not work.

Instead ESR recommended ground-truthing:

"... visual inspections of the sites are highly recommended in providing as much detail as possible on which informed decisions can be made. Because of the complex interaction of faecal source, land topography, soil type and climatic factors, one solution will not be suited to, or effective for, all sites. A site-specific solution that considers these various factors will yield the greatest benefit. Mitigations should be prioritised based on risk assessments that identify priority areas for improvement, whilst also considering which strategies provide the greatest return on investment".

Federated Farmers critiqued many aspects of the Governments proposed freshwater package. But on the importance of monitoring data and prioritised Action Plans, we are on the same page.

Others have criticised "bottom-up" monitoring and Action Plans as "soft options", instead favouring "top-down" limits and regulation.

These results from Southland suggest the top-down approach would be hit-and-miss at best.

If we are serious about meeting our swimming targets – or our ecosystem health targets – there is no substitute for site specific data and catchment-specific action.