Out of the Blue

The other test that we do on the River Walks are Methalyne (Meth) Blue tests, which indicate oxygen levels in the water.  We stain a sample of water with Meth Blue (actually, it is the oxygen that gets stained). If there are bacteria present, the bacteria will eat the oxygen and the blue colour will fade.

penny data recording lidgetton

The time it takes to fade indicates the levels of oxygen in the water, (and conversely  indicates bacteria as well).  For example a sample that fades in 24 hours or less has no oxygen (and a very high bacteria load), whilst at the other extreme, a sample which does not fade after 5 days has 100% oxygen ( and few bacteria). Simple as a pudding! Hence the delay in getting this blog out – I have been checking the Meth Blue samples each evening.

The Meth Blue samples have indicated the following levels of Oxygen:

Sample 1: 40%

mb Site 1

Sample 2: 80%

MB site 2

Sample 3: 90%

MB site 3

Sample 4: 90%

mb site 4

Sample 5: 90%

mb site 5

Sample 6: 60%

mb site 6

Sample 7: 80%

mb site 7

Remember that minSASS is a general indicator of river health, whilst Meth Blue helps explain or eliminate bacterial infection.

The big thing when looking at these samples is to remember that:

  • The Miracle: mentioned in the previous blog: Rivers can heal, but this is no excuse to contaminate or impact them. To heal they need a long enough stretch without impacts, or they will not heal.


  • Wetlands clean rivers – the roots of the plants actually absorb pollutants and aid in “polishing” the water. If the pollutants are too many for the size of the wetland, the wetland cannot polish the water source.

Source reccee (16)

  • By keeping the river buffer area (32 metres wide from the edge of the water) in a natural state and clear of non-indigenous plants, rivers are healthier


(many of the kikuyu pastures we have seen on our walks are historical – in other words they were established decades ago when we did not understand the importance of a “pristine” river bank and river buffers were thus not implemented)


River walks are full of surprises and we have learnt to expect the unexpected!


If you are keen to do something to help heal our desperately sick rivers, please remember that March 14th is International Day of Action for Rivers. If you’d like to contribute on that day, please send us a comment and let us know what you plan.

Int day of rivers 2014 logo

From the Mayday for Rivers Team – thanks for your interest and support. We are planning the next walk already – watch this space.



About Nikki Brighton

I live in Howick, between the river and the hills. I enjoy pre-dawn walks in the streets with my dog, sitting on the veranda with crochet and tea, and harvesting vegetables outside the kitchen door.
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One Response to Out of the Blue

  1. Julia says:

    Hi Guys, It looks like you are doing a fantastic job whilst having a lot of fun. I would be keen to do that blue methalyne tests at my own schools. It is simple to do with clear results. Where can i buy meth blue kits from?

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