Water pollution? or iron oxide bacteria?

Is it ok to empty swimming pools into the storm water system?

Swimming pools contain chlorine or salts to kill off things you don't want in your swimming pool.  If they get into the Le Roys Bush streams, they will kill off the inanga, kokopu and other native acquatic life. 

Is it ok to wash a car of a driveway or street?

If detergent or oils get into the Le Roys Bush streams, they will harm the inanga, kokopu and other native acquatic life. 

Can I let my dog swim in the Le Roys Bush Streams or Wetland?

Dogs can frighten the fish and also flea treatment may harm the fish.  Please wait till you get to the beach!

What is the orange rust coloured water in LeRoys Bush?  

Many people walking through Le Roys Bush from Onewa Road to the waterfall wonder what the bright orange rust coloured pool is on their right. (By the way, the pool has been this colour for at least 30 years - older residents may be able to tell us when they remember it first being like this).

The following answer was provided by the pollution control officer in the Environment Division of the North Shore City Council in 2008.
  • Iron oxide bacteria can appear as a bright orange rust coloured layer of either fluffy or slimy material on the bed of a stream in a slow flowing area, at the base of a storm water pipe, or as an orange stain on the ground. 

  • There may also be a layer of what looks like oil in association with iron oxide bacteria.  This is a by-product of iron bacteria metabolism.  The test to tell it apart from petroleum-based oil is easy: dip a stick into the middle of it and swirl it around to break it up; the man-made oil will quickly stick back together (I describe it as the “Terminator effect”) whereas the natural oil will remain broken up into shards.

  •  Sometimes a layer of iron oxide bacteria can release from the bed of the watercourse and flow down stream due to a bacterial die-off or changing environmental factors. 
  • Iron bacteria is common throughout North Shore City and is not known to pose any human or environmental health risk.  It occurs naturally all around the region as a result of elevated iron content in the soil.  Sometimes iron bacteria can indicate fill containing metal elements such as old white-ware or a car body. 
If you would like more detail…
  • Iron Bacteria are a group of small unicellular organisms which grow in chains and excrete a mucilaginous sheath. This sheath becomes light brown from iron oxide and appears as a fuzzy coating on any available substrate. Iron oxide is formed as the bacteria oxidises ferrous iron to ferric iron. The ferric iron becomes iron oxide when it is exposed to air and water. 
  • They are indicative of iron rich water, ground water seeps and low flow conditions. These waters are often acidic or in contact with an anaerobic sediment layer because ferrous iron is favoured in these conditions.

Postscript: Some of the people who work around the bush have noticed that this activity appears to be more common below the outfall of old stormwater pipes.  Although more research needs to be done, they wonder whether there may be iron content in some of the old pipes which gives rise to this phenomenon.