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.
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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


