What happens to the rivers when people stop?

As New Zealand was preparing to close its doors in the last week of March, Christchurch-based freshwater advocacy group, Drinkable Rivers, seized a unique opportunity to examine the tangible effects of lock-down on our waterways. The day before New Zealand entered Level 4, the team took the first of two water quality samples from the Ōtākaro/Avon River within Christchurch CBD. A follow-up test was then performed at the same site nearly 5 weeks later as restrictions eased and the nation moved into Level 3.

At first glance, the results showed some potentially exciting reductions in E. Coli, Lead and Zinc during the lock-down but, given the myriad factors impacting water quality, how should these numbers be interpreted? Globally, many others hoped to see similar improvements as a result of their local lock-downs. With dramatic claims about water quality improvements in the Ganga River later walked back by India’s Central Pollution Control Board, the Drinkable Rivers team acknowledged that interpretation is key and sought some expert analysis of the data.

Christchurch freshwater scientist Phil Clunies-Ross agreed that lock-down posed a “truly unique opportunity to examine the Avon during a time when our influences on the river may change significantly”. He noted that some specific areas where we likely could see improvement would be in reduced quantities of sediment entering waterways through human activity, as well as reduced concentrations of trace elements entering waterways due to lower industrial activity and fewer vehicles on the road. He also noted, however, that any direct interpretation of the data is tricky.

“From my experience, water quality sampling and analysis can be notoriously difficult, with various pressures (such as the weather) having significant influences on the biological, chemical and physical characteristics of the water. It can be very difficult to draw any conclusions from a limited number of samples... Compounding the difficulties in analysis is the ‘lag’ period, where changes (positive or negative) in water quality may not become apparent for long periods of time.”

He also noted that, in fact, a reverse correlation could be possible, where concentrations of certain contaminants such as E. Coli – one of the more notorious waterway pollutants – could have actually increased in lock-down due to activities that are very difficult to measure. E. coli levels are known to be quite variable in urban water samples; these results could be showing impacts of numerous potential sources which can contribute faecal contamination to the river at any time. These might include an increase in people walking dogs along the riverbanks or feeding birds in their local waterways during lock-down.

So what do we know for sure? The E. Coli results of both tests are higher than 550 cfu/100 mL which is the level that is considered to trigger Action status under the Ministry for the Environment/Ministry of Health 2003 Recreational Water Quality Guidelines. This indicates that the Ōtākaro/Avon River remains in the Poor category for primary contact recreation sites; in effect, unswimmable.

Ultimately, for Drinkable Rivers, this leaves only one certainty: there is still a lot of work to be done. Even a complete halt on regular daily activity as we saw in Level 4 (unless, perhaps, over a much longer period) is likely not enough to meaningfully improve our waterways. Our businesses and residents need to be actively working together on conservation and restoration efforts if we hope to get our rivers swimmable, let alone drinkable.

The good news, notes Clunies-Ross, is that the manual tests support the real-time readings currently being taken by Drinkable Rivers’ prototype water quality measuring device, Oracle 1. “Correlating these results with other datasets (such as rainfall events) could help to tell a story on the external influences of water quality in the system,” and, in doing so, further Drinkable Rivers’ mission to give our rivers a voice.