Owhiro Bay water quality

Update 29 May 2020

Wellington Water monitors environmental water quality to detect contamination which may indicate problems within the network. This update is to inform the community of latest result and current activity in the area.

All samples are gathered and analysed by an independent specialist laboratory.

Latest sampling results



Update 8 May 2020

Owhiro Bay results 4 may

During the response to COVID-19 with many activities on hold/paused at alert level four, it was requested that we undertake sampling in Owhiro Stream to see what impact this paused activity had on the stream. We continued this through the transition to alert level three.

For reference, the sampling site ‘Owhiro Stream above T&T Landfill’ is located above most of the commercial activities, whereas the sampling site ‘Owhiro Stream at Happy Valley Tip Bridge’ is at the intersection of Rarangi Road and Happy Valley Road – which is below most of the commercial activities centred around Landfill Road. At these sites, the sampling results were below the consent pollution response triggers.

At the sampling site, ‘Owhiro Stream behind 17 Happy Valley Road’ is a freshwater monitoring site that is just upstream of the Owhiro Bay Parade bridge. It was chosen as it has less tidal influence than the Parade Bridge site. The results show that on most days, the pollution levels here were higher that the sites around the commercial activities. The results were higher than consent triggers in three occasions. This would indicate that the pollution is likely coming from a source(s) below the commercial/industrial activities. As with Alert Level 4, we are concentrating our resources on essential services and on keeping our frontline teams, who maintain them, safe and healthy. Our water quality monitoring and response activity continues to be scaled back during Alert Level 3.

The latest results show high levels on May 3 and 4, this is a result of heavy rainfall. As always, it is recommended that you don’t swim 48 hours following heavy rainfall.


Update 15 April 2020


The Baywatch site has been in green since January. The stream mouth quality has been improving since 27 March, which is likely due to the heavy rainfall we experienced a couple of weeks ago giving the whole stream and stormwater network a good flush. 

Update 6 April

update 6 April

Readings have trended down as the system flushes out after heavy rain in the last weekend of March.


Update 3 April

3 april

Readings are typically higher following rain because it washes contaminants into the stormwater system and stirs up pollutants already stuck in pipes. The high results here are a result of the heavy rain we had last weekend.

You may have noticed a difference in some of the sampling results, with results higher than 10,000 showing as >10,000. This is because we moved to a test with a more rapid turnaround in order to provide results within a shorter timeframe for the Owhiro Bay community. This test provides precise results up to 10,000. Precision above that level requires the longer turnaround form of testing.

In the context of the national response to Covid-19, our top priority is providing clean drinking water and safe wastewater treatment to our community. This means our water quality monitoring and response activity is being temporarily scaled back. Read more about our response here.

What the lock down means for sampling in Owhiro Bay is that we are essentially reverting to our regular sampling programme from Monday 6 April. This means:

• Sample testing at the recreational bathing Baywatch site in Owhiro Bay will be fortnightly from April 1 with the end of the bathing season
• Because we are suspending work on private cross-connections during the lock down, we will suspend associated sanitary survey sampling in the stream
• Samples from the bottom of the stream will be taken fortnightly rather than daily
• The other sites in the stream will be sampled monthly rather than daily
• We’ll change our sample test from the quick-turnaround test accurate up to 10,000 cfu/100ml back to the longer format test that captures spikes into the millions, should they occur. These samples take an extra day or so to process but will allow us to better detect blockages causing wastewater overflows that require urgent attention.

Update 30 March

30 march OB

Results have been affected by rain and therefore inconclusive with regards to helping narrow down the source of the pollution.

Update 27 March

27 mar

Rain on Tuesday will have contributed to the high values we’re seeing.  However, levels at the stream mouth and the Parade Bridge are still a concern. Rarangi Way culvert has not been out of spec since the cross-connections were fixed on 11 March, so we are investigating the lower section of the stream.

Update 24 March

24 mar update

High results for the stream outlet were likely due to rain on the night of the 21st. We have started sampling from the bottom of the stream moving up to find a possible source nearer the bridge.


Update 20 March

18 19 Mar2

Rarangi Way culvert results are trending down, indicating that the work that Wellington Water drainage teams have undertaken in that area is having a positive effect on water quality. However we are seeing some higher results at the stream mouth and Parade Bridge. This suggests a possible issue in the lower reaches of the stream closer to the bridge, which our teams are investigating. Notably, the sampling sites in the bay itself continue to show good results, indicating that the issue at the stream mouth is not extending beyond the bay into the Marine Reserve.



Update 19 March

Owhiro Bay sample results 19 march2

The latest sampling indicates the stream mouth is back at unsafe levels, as well as the Baywatch site at an amber level. These results may have been influenced by the stormy weather that came through the night ahead of this sampling. We are continuing with investigations in Owhiro Bay to locate further contamination points.

We will look at the next samples as they come through, which will give us a better indication of what’s happening in the catchment.

Update 18 March

Owhiro Bay results 17 March

Readings are a valuable measure for establishing faults and trends, but because they are a small sample taken at one moment in time they do not indicate the state of the entire waterway all of the time.

Readings will vary for several reasons. Wastewater flows are intermittent in nature, depending on how the community is using water at the time – for bathing, cleaning, laundry, using the toilet and cooking. Peak use time is between 7am and 9am, so a reading taken during that period might result in a spike. Sea conditions affect readings, and readings will always be higher after rain because it washes contaminants into the stormwater system and stirs up pollutants already stuck in it. For this reason, swimming at urban beaches should always be avoided 48 hours after rain.

Sample readings are presented on a logarithmic scale because there are exponential changes in the magnitude of numbers.

A swimming beach reading of 280cfu/100m leads to the beach’s closure and an investigation to stop the pollution source. (Cfu stands for colony-forming units, in this case the microorganisms being measured are live bacteria found in bird, human and other mammal faeces.)

Most urban streams are not swimmable and processes around readings are different. Current monitoring is based on a rolling 12-month median value for E.coli (dry weather sample) > 1000 cfu/100ml, which triggers investigation on the ground, as well as a single reading above 10,000 cfu/100ml/
A stream reading above 1000 cfu/100ml requires that a second reading be taken the next day. We are migrating towards Greater Wellington Regional Council’s Global Stormwater Consent condition of two consecutive samples of >1000 cfu/100ml, triggering investigation on the ground. This will be closed out as part of 21/31 LTP discussions.

To put those sample numbers in context, a single reading of over 20,000 cfu/100ml is not unusual for urban waterways in Wellington or across New Zealand, particularly after rain. The top end of the scale is raw sewage, which reads in the millions. 

Update 11 March - recent sampling results

The sampling results published on 9 March indicated a spike in results on 1 March of 23,000cfu/100ml.

While this spike understandably caused concern in the community, we think some more context will help to address this. These figures are not uncommon across the Wellington region and across New Zealand after rain. Rain will wash pollutants into the stormwater system and will stir up pollutants that accumulate in the stormwater system over the very dry summer. This is why our advice is always to avoid swimming at our beaches following 48 hours of heavy rain.

We will be discussing these results and related matters at the Community Board meeting on Monday 16 March.

We are really grateful to the community for their interest in this work, and we’ll be providing more context for this and the test results in the future on our website: wellingtonwater.co.nz/owhiro-bay

Update 11 March - stormwater flushing

We’re flushing out stormwater pipes in the Owhiro Bay catchment today. This is to help clean out pipes that have been affected by the plumbing faults (cross-connections) that we’ve found and fixed.

We believe there is more work to do, so we will be continuing with our investigations in the catchment.

One of the ways we investigate is through dye testing. Dye is put down the gully trap (plumbing feature that receives wastewater from the property) of a property, and if the dye comes out in the stormwater network, we know there is a plumbing fault. Dye testing will be continuing over the next few weeks.

Update 9 March

Owhiro Bay 9 March

Update 2 March

Owhiro Bay Monitoring 28.2

Update 27 February

Owhiro Bay 26 Feb

Update 21 February

Owhiro Bay sampling 19 Feb

Update 19 February

We are currently undertaking water quality sampling in Owhiro Bay; daily at the stream mouth, and weekly at the Baywatch site (on the other side of the bay).

Below are the latest results.

Owhiro Bay sampling2

Update 4 February

We have followed our protocols recommending the reopening of the beach. A source of the spike in contamination was identified and the sampling at the long term beach monitoring site had returned to normal. We acknowledge that our communication could have been better as removing the warning signs implies that the Owhiro Stream, that crosses the beach, is safe for swimming in. Owhiro Stream, like many urban waterways, has a long history of contamination and is regularly unsafe for swimming in. Improving the quality of Owhiro Stream will require a coordinated and long term programme of works.

We have identified water quality as one of our key focus areas for our client councils to consider in the preparation of their upcoming Long Term Plans. In the short term Wellington Water will implement a permanent sign at the mouth of the Owhiro Stream warning people of the potential water quality issues.

Update 30 January

The beach has returned to safe levels and our investigations of the likely sources in the catchment has just been completed with 3 cross-connections found. We will be removing the warning signs today.

Thanks to the wider community for your patience and understanding as we worked through resolving these cross-connections.

Update 29 January

Our operations team have been hard at work resolving cross-connections in the network. As a result of this work, we are seeing an improvement in the water quality in Owhiro Bay.

We are continuing with our routine sampling, and are looking at when it is appropriate to take down the warning signs. For now, they are still in place. We will confirm when signage comes down.

What's happening?

The water quality in Owhiro Bay is being affected by a cross-connection. A cross-connection is where a wastewater pipe is connected into a stormwater pipe. Most cross-connections are from private pipes into public (council) pipes, and this is the case here. Wastewater from private properties is entering the stormwater system, which leads to Owhiro Stream, which leads to the Bay. We are working with the property owners concerned, who were not aware of the issue, to resolve it as quickly as possible.

Contamination from cross-connections can be difficult to locate. Wastewater flows are not constant - they depend on usage. To find the source we have to take samples, send them to the laboratory for testing, and then get the results. This takes a couple of days. We have to work our way methodically upstream to narrow down the area where the contamination is coming from.

We're working with property owners to resolve cross-connections we've identified. We expect to have these sorted by the end of the week. We're also continuing our investigation and testing; it can be a mistake to think the first fault you come across will fix the problem.

If you have concerns about what you think might be a cross-connection at your place, please let us know and we'll come and take a look. Our main concern is to eliminate as many of these as we can.

Warning signs that recommend against swimming and fishing in Owhiro Bay remain in place, and will stay there until we receive three consecutive days of clear results. We will update via social media and the website when this changes.

If you have been swimming in the area and feel sick, please visit your doctor.