More than fifty Auckland beaches were deemed unsafe to swim in over the Christmas-New Year period, disrupting the plans of thousands of summer beach-goers. So why were the beaches polluted in the first place?
The stormwater system is designed to collect excess water when it rains. During intense rainfall such as those we experienced this summer, the pipes can become overwhelmed causing water to backflow into sewage pipes. The stormwater then mixes with sewage before it is discharged into the streams, eventually running into rivers and out to the sea.
The presence of sewage in the streams can cause other problems too. Sewage contains nitrates which can feed the algae in the water to result in an overgrowth in algae (algal bloom). These blooms can causes several problems to the ecosystem and water quality. One is that the overabundant algae can block out the sunlight to other organisms that need light to survive. Another concern is when the excess algae start to die. It creates an increase in bacteria to breakdown the algae. Unfortunately, the bacteria utilize a lot of oxygen and can deplete the water of oxygen rendering some waterways unfit for any aquatic life. Some algae release a toxin when they die, which can be absorbed by filter feeders such as shellfish. This toxin magnifies as it moves up the food chain, resulting in poisoning the animals and humans that ingest it.
The best time to test the stream water is after a heavy rainfall. Although it is summer, the ‘La Nina’ weather patterns are causing warmer and wetter days for the northern part of New Zealand. The more rain in Auckland, the more we should be concerned about our waterways.
The Whau River Catchment Trust test the water of various streams within the catchment. If you would like to join in the stream water testing or just observe and learn how to test the water, contact Justine via email: firstname.lastname@example.org or text 021 627864 for more details. The next testing date will be on the Saturday 13th February 10am. The destination is yet to be confirmed. If you cannot make that date, there will be more stream water testing events coming up.