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Water quality of stream at northern end of Snells Beach

Updated: Jun 6, 2023

The stream that enters Kawau Bay at the northern end of Snells Beach doesn’t have an official name, that we know of. Hopefully one day we remedy that but for the time being it is referred to as Snells Beach stream.

It captures water from the north-western hills of Snells Beach and meanders downhill through some bush and a few ponds. Then, it goes underground through a long culvert, comes out at Whisper Cove, and drops into the saltwater wedge and winds its way to the beach.

Recently Snells Shoreline Conservation Community decided to monitor the water quality and test for species living in the water.

Water quality testing - November 2022

The first water quality monitoring session was conducted in November 2022. Snells Shoreline Conservation Community have committed to at least four tests per annum, with the next one due in February 2023. The first effort informs us that the stream carries only trace amounts of nitrates and phosphates, which although not perfect is promising.

However, there are other factors that affect the health of the stream, water temperature, clarity, and dissolved oxygen and all these parameters were below par.

A major indicator of the health of the stream is the number of macro-invertebrates in the stream. These are greatly affected by the water quality parameters. This stream sustains macroinvertebrates that can cope with poor water quality, such as water fleas, worms, mosquito and sandfly larvae, and some types of snails.

Macroinvertebrate that prefer better conditions than Snells Beach stream allows, would be mayfly larvae, dragonfly larvae, caddisflies, pond skaters, water boatman, molluscs, kōura, and many more.

eDNA testing at Snells Beach - November 2022

To identify other species in Snells Beach stream we can assess the DNA. Snells Shoreline Conservation Community obtained an eDNA kit from Wai Tuwhera o te Taiao, the Environmental Protection Authority. The results are fascinating and confirmed our suspicions from our own monitoring.

First, the good news.

Banded kōkopu egg at 21 days
Banded kōkopu egg at 21 days

The stream is supporting two of New Zealand’s native whitebait species – inanga

and banded kōkopu. Both species are in decline. Inanga spawn in the saltwater wedge just below Whisper Cove and the banded kōkopu, upstream, probably in Brick Bay winery.

Long fin tuna/eel swimming
Endemic long fin tuna/eel

There are tuna (short fin eels) which are a native species that are highly adaptive.

More important is the presence of endemic long fin tuna, which is only found in New Zealand. They are the largest eel in the world and are currently classified as At Risk – Declining by the Department of Conservation.

There are also some pests, mosquito fish and goldfish and the eDNA test also showed that there is a shortage of macroinvertebrates.

The overall ecological health score was also poor.

Person taking photo of long fin eel in a stream.
A curious long fin tuna eel in a freshwater stream at Snells Beach .

In summation, the stream lacks biodiversity, which means a lack of variety of native species and in particular macroinvertebrates. There are probably several contributing factors and the major contributing factors are:

  • high levels of suspended sediment

  • low levels of dissolved oxygen

  • exposed surfaces to sunlight

  • higher water temperatures

Snells Shoreline Conservation community will continue to monitor the stream water to assess the impact of conservation work. However, it is anticipated significant changes will take some time.



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