THE BROWN WATER IN FALSE BAY

Articles are being written in the Cape Town press on a regular basis, or whenever the phenomenon occurs. Often a nearby sewage plant is blamed. However, the dirty brown water is perfectly safe. See the article below, which was published in 2006 and which will set the record straight:

THE BROWN WATER IN FALSE BAY

The most popular misconception is that the brown water phenomenon is caused by raw sewage discharged into the sea. Ironically sewage is not brown, it rather resembles the grey colour of waste water from a washing machine. Extensive studies of the patches have however established that the discolouration is caused by the aggregations of ten of thousands and sometimes millions of single celled plants known as diatoms. The organism has been identified as Anaulus Australis. It is unicellular and occurs naturally in the surf zone along sandy beaches.

Anaulus Australis has been monitored by the Scientific Services Department of the City of Cape Town since 1989 on a fortnightly basis along the False Bay coast between St. James Tidal Pool and Mnandi Beach East. There are a total of twelve sample points on which Anaulus counts are done. The highest concentrations are found in the area between Sunrise Beach and Life box 30.Trends based on the median values of all the sample points indicate a drop in the number of cells counted this past year. As can be seen by the accompanying graph, there has been no great variation in the numbers over the past twelve years. Anaulus Australis is not a pathogenic organism and does not pose a health risk to bathers despite the obvious aesthetic aspect of swimming in "dirty" brown water. Apart from the Western and Eastern Cape, sightings have been reported worldwide, including the Mediterranean Sea,

California, North Islands of New Zealand and the Hawaiian Islands (CSIR, 1989). Physical and chemical factors, which control surf diatom blooms, have been identified as nutrients, silicon (obtained from freshwater input from adjacent dune fields), currents, temperature and wind. The only way to limit the occurrence of brown water patches would involve an attempt at modification of these natural factors. Research has confirmed that treated sewage effluent discharges into False Bay are not a requirement for the formation of Anaulus patches.