The return of warmer weather in recent weeks has lured many Adelaideans back to the coast – ready to embrace the beach culture that we so love in summer. If you were among the walkers or swimmers, perhaps you too have been appalled by the colour of the water – a huge unappealing brown slug hugging our favourite beaches.
The cause is a cocktail of silt and other pollutants that has been pouring out of the creeks and many stormwater drains that empty onto the coast for decades. The incoming and outgoing tides mix and spread this pollution – but only a bit. Water in Gulf St Vincent does not move extensively – it basically sloshes in and out (up and down the Gulf), so the pollution radiates slowly away from its source.
In still conditions, the silt settles out, and water quality can be pretty clear. When windy weather hits, the silt is remobilised – stirred up – and the water becomes brown once again.
Depressingly, this layer of gunge is now a permanent feature of the Adelaide metropolitan coast.
But the story is more complicated…