Dye testing of the Collingwood St wastewater and stormwater systems

Clean Swimming Holes

Testing of the Maitai River at Collingwood St Bridge, and the Collingwood St wastewater and stormwater systems has shown a complicated picture. Background E.coli levels in the river over winter are pleasingly low, and somewhat higher in summer but still mostly below alert level. The amber alert level was exceeded 10 times over the course of the year, but the red alert level was only exceeded once.

The E.coli in the river is from ruminant, wildfowl, gull, human, dog and possum, so the E.coli levels detected are not just related to human activities. However the dye testing of the pipes has shown that there is definitely some leakage from the wastewater system into the stormwater system even in dry weather, which may be affecting E.coli levels in the river. This is being fixed where possible, and we have a budget for this year too to continue with locating and fixing issues between the wastewater and stormwater networks within the central business district. Hopefully we’ll see sustained improvements in the E.coli readings at the Collingwood St Bridge swimming hole over the next few years!

In the meantime people are advised not to swim in the river if the water is discoloured, especially for the first 24 – 36 hours after rain when surface runoff can cause contamination. If you’d like to see summertime testing results from your favourite Maitai swimming hole please visit https://www.lawa.org.nz/explore-data/nelson-region/river-quality/maitai-river/. Roll on summer swimming and picnics!

The new automated cone discharge valve at the Maitai Reservoir

A Healthy and Natural River

Changes have been made to the way the Maitai Reservoir is operated to reduce the impact on the Maitai River. A new valve has been installed which allows de-oxygenated water from the lower levels of the reservoir to be aerated before it enters the river. This valve only functions when the river levels are high so that any effects from the reservoir water on the river are minimised by the increased flow. When the flows are lower good quality water from the top layers of the reservoir are discharged to the river to compensate for water removed from the South Branch for city water supply.

York Stream Bishopdale Reserve stormwater inlet chamber showing concrete section removed and spat rope fish ladder on concrete step.

More Fish and Stream Critters

Sometimes the only way to make infrastructure fish-friendly is to cut a hole in it! Fish passage improvements have been made in the Brook and York Streams, and boulders and logs have been placed in Pipers Reserve Stream and York Stream at Victory School to make the streams a better place for fish to live. More work is planned to improve the Brook Stream concrete channel and some concrete lined sections of York Stream.

Anna Berthelsen from Cawthron Institute sampling Saltwater Creek sediment

Fixing Saltwater Creek

The purpose of this project was to address water quality issues in Saltwater Creek through a combination of infrastructure, compliance, science, behaviour change and community-led projects.

Our surveys show that people care greatly about the health of Saltwater Creek and about the importance of healthy waterways generally. Many did not know that the stormwater system goes directly into the creek, and there were some great stories from people who remember the creek before it was covered over.

Sadly the science has told us that the Saltwater Creek sediment is really quite contaminated, although much of the contamination is probably historical and has just remained there. The clean-up days and installation of new bio-filtration swales in the Rutherford Park carpark are helping to reduce pollution inputs, and there is some life in there, so it could still be an attractive tidal creek in the future. Some consideration needs to be given to what to do next, and in the meantime we’ll continue with efforts to reduce the pollution and litter getting into the creek.

More Riverside Planting

Nelson Central School students and helpers planting alongside Brook Stream

There were nine new riverside plantings in the Maitai catchment this year, including large trees along the lower Maitai Walkway, a public planting below the Maitai Camp, Council plantings in the Maitai Valley near Sharland Creek and a variety of volunteer plantings.

The Friends of the Maitai have continued to plant and care for their area near Groom Creek which is looking lovely, and Nelson Central School have adopted the banks of Brook Stream near their school. School parent Liz Gavin from Canopy Landscape Architects initiated the project and the school has embraced the idea. The children have been learning about caring for their local stream, through identification of invasive weed species, litter collection, and planting of over 400 native plants that will help shade the stream. Their efforts will improve the quality of this urban waterway, and enhance it as a habitat for native fish and other wildlife. Well done and many thanks for all the hard work!

Toxic algae in the Maitai River

Less Toxic Algae Risk

The best news from this project is that there were no dog fatalities over the summer and no public alerts were issued because the levels of toxic algae cover didn’t exceed the trigger levels.

Cawthron institute carried out four research projects which confirm that flow, nutrient and sediment levels are important factors in promoting cyanobacterial blooms. There is also an indication that conductivity and river microbial ecology (especially relationship with other algal species) might have a role in the occurrence of blooms. A large amount of data has been gathered and we are applying for funding to analyse the data and get some guidance on possible interventions. A further study to identify the source(s) of fine sediment in the river is also planned.

Upgraded Maitai Track

Fish Barriers Removed (Maitai/Mahitahi Ford Improvements)

As part of the Maitai Fords project the Maitai Track has been upgraded near the Golf Course so there is an option for stock and utility vehicles to use the track to access the Groom Creek Bridge rather than going through the river at the Almond Tree Flat ford.

The Almond Tree Flat ford is now the last major fish barrier on the Maitai River after the fish barrier at the Waahi Taakaro ford was fixed earlier in the year. Several options for modifying the ford to allow year round fish passage were investigated but none are suitable because they are not strong enough, or will still need ongoing maintenance, or there is a risk they will alter the downstream river path. So we have done some surveys to find out what people would think about removing the ford.

The studies included on-site user surveys, on-line public surveys and a track counter. Overall 134 people took part in the on-line survey. Altogether 76% of on-line survey responses supported the removal of the ford to allow fish passage, which was very heartening. 16% wanted the ford to be kept as it is, 5% had no opinion and 3% thought Council should adopt the lowest cost option.

Once the results have been fully analysed, a recommendation about the future of the ford will be made to Council for a decision, so we’ll let you know the outcome later this year.

Project Maitai/Mahitahi page in the Nelson Leader

Get Involved

Have you seen our new look page in the Nelson Leader? It comes out once every two months with some stories about what’s happening in Project Maitai/Mahitahi. We also have information on our website at www.projectmaitai.nz and the Friends of the Maitai website is also a good place to look for ways to get involved friendsofthemaitai.org.nz. This year we’re starting two new projects which will have some great opportunities to get involved and take some action for your favourite waterway. In the meantime, if you are interested in adopting a stretch of your local stream, or taking part in periodic stream clean-ups or streamside plantings, or you have any other great ideas for taking action please contact us, we’d love to hear from you :)