Not what it used to be.

Toxic river algae alert! A sign I have been seeing a lot in the Hutt Valley over the past 10 years. As a child, a summer tradition was to venture down to the river and go for a swim. I was a small, skinny child so getting into cold water was always such an effort. Each year I became more confident getting into the water. But when I was finally comfortable being submerged in the cold water, the river suddenly became covered in a mat of toxic algae and was no longer suitable for swimming. I was once told that the algae came from other rivers that was brought here by the horses involved in the filming of The Lord of the Rings but I think that was just hearsay. Recently, I read a blog post highlighting the causes of waterway pollution and was briefly reminded about the toxic algae that has been present in my local rivers and I wanted to know more about it. What is it? And why is there so much of it?

Algae is a made of many microorganisms called cyanobacteria. It is an aquatic organism that feeds via photosynthesis. It forms black or brown mats along the river bed covering most rocks. When I visited the river whilst the algae had no toxicity warning, it felt slimy, smelt dreadful and was very slippery to step on. When detached from the rocks its floats along the surface of the water; if exposed to dry conditions the algae will dry up and produce a musty odour.

http://www.radionz.co.nz/assets/news/11898/eight_col_ALGAELR.jpg?1387412678

Favourable conditions for extensive algae blooms include warm temperatures, sunlight, a low or stable river flow and nutrients. Being a type of bacteria, it thrives in warmer conditions. This is why the toxicity levels are much higher in summer months as the temperature of the water increases. Nutrients for the algae mainly include phosphorus and nitrogen. The presence of nitrogen in the waters is mainly due to nitrogen rich urea found in animal urine. Phosphorus is found in the ionic form phosphate, which clings to soil particles that wash into the river forming sediment. This makes the Hutt Valley River a perfect environment for Algal blooms to thrive.

The toxicity of the algae can kill dogs and livestock in less than an hour in extreme cases. Symptoms after ingestion can include lethargy, muscle tremors, fast breathing, twitching, paralysis and convulsions. This is a very cruel way to watch your beloved pet pass. In humans, symptoms of algae ingestion are not normally as severe but can include skin and eye irritations, gastrointestinal disorders, cramps and diarrhoea. Of course the concentration of toxins in the water do contribute to the symptoms that may develop but it is recommended to stay away from the river altogether.

It is so unfortunate that the algae blooms have made their way into my once great swimming locations. It makes me curious as to where such a toxic cyanobacteria came from in the first place. Was it always there? Does increasing pollution and temperature rises contribute to the increase of the toxic algae bloom in the river? I am constantly saddened and frustrated that the river is no longer a destination I can go to in summer.

Dangers of toxic algae . (n.d.). Retrieved from Environment Canterbury Regional Council: http://www.ecan.govt.nz/services/online-services/monitoring/swimming-water-quality/Pages/toxic-algae.aspx#causescyanobacteria-algal-blooms

Wright, D. J. (2012). Water Quality in New Zealand: Understanding the Science. Wellington, New Zealand. Retrieved from the Parliamentary Commissioner for the Environment: www.pce.parliament.nz/media/.../pce-water-quality-in-new-zealand.pdf