Published 13/02/2020
Whairepo Lagoon water quality update – Thursday 13 February
Water quality test results for Whairepo Lagoon show it is currently safe to swim there and in other areas of the inner Wellington Harbour except for the Taranaki diving platform – but swimmers should always be aware that this could change, and treat the water with caution.
We apologise to members of the public who may have been left confused by media reports that there was any doubt over this situation. In this instance, we had not kept the Council fully updated on daily water quality test results.
How confident can we be the water is safe to swim?
Water quality tests are carried out directly where people are swimming, in accordance with protocols agreed with Regional Public Health and Greater Wellington Regional Council authorities. Water samples are taken and analysed weekly during summer, and whenever there is a higher risk of contamination samples may be taken daily. In this instance we are undertaking daily sampling for the next week. It is important to be aware test results take 24 hours or more to process.
Water quality in the inner harbour and urban beaches is affected by the quality of stormwater that drains into the sea. After rain, Wellington Water and Regional Public Health recommend swimmers don’t go into the water for 48 hours. This is because surface run-off city streets and streams contains contaminants that could make people sick.
The Taranaki diving platform is unsuitable for swimming due to most recent sampling results.
How does the water get contaminated?
It is important that people understand that the stormwater and wastewater networks are not completely secure. There are cross connections between the two systems. Historically, some of these crossover points were designed on purpose; they were built as a kind of failsafe in the event of a wastewater pipe blockage, to divert backed-up water into stormwater pipes and keep it out of streets and homes.
This is not an ideal situation, but it is the way things were done in the past, and for now, we have to deal with it the best we can. It means that there is always a risk that stormwater outlets can contain contaminated water if there’s been a pipe blockage – for example due to wet wipes or fats, or a pipe collapse.
There is an additional risk of contamination, from unplanned cross connections. These occur as a result of private wastewater pipes being connected to public stormwater pipes. This can arise through illegal or poor workmanship, as a result of incomplete records, or through genuine mistakes. Cross connections can go undetected for years, despite water quality monitoring. This is because of the way stormwater and wastewater networks operate. The flows they care are neither constant nor steady, so water quality results at the outfall can be inconsistent.
What are we doing about it?
Underground infrastructure management is complex, and expensive. In Wellington, councils do their best to ensure that water quality meets modern expectations, but often, they must do this with infrastructure built back in the day when standards were lower. We’re working to improve things, but as is often the case with networks, the whole system is often only as strong as the weakest point.
There is always a risk present when swimming or interacting with water in urban streams and near stormwater outfalls. The best way for members of the public to manage this is to rinse off with clean water after they’ve been playing or swimming in these areas, and take special care with any skin wounds. In the first instance, it is advised the public check LAWA map at lawa.org.nz.
The more that people are aware of this complexity, the costs, and the risks involved, and how they can work with them, the better.