A fishy stench has been drifting across the Mackay coast this week, leading locals to wonder what is causing it.
But rather than the sinking of a manure ship carrying a load of stink beetles, the source is much more natural and interesting. Algae.
A series of algal blooms off the coast have been washing ashore and breaking down, wafting the stomach churning smell across the tropical north coast.
Researcher with the Australian Institute of Marine Science (AIMS), Barbara Robson, said this kind of algal bloom is common in early spring in the tropics.
"Trichodesmium is a naturally occurring blue-green algae that occurs in marine waters all over the world especially in the tropics," she said.
"It's very common in the great barrier reef and this time of year is when we most often see these surface blooms."
But she warns the algae, commonly known as sea sawdust, like other blue-green algaes, is toxic for humans.
"Trichodesmium can be toxic," Dr Robson said.
"I wouldn't go swimming if there is a visible bloom in the water.
"The toxicity is probably not quite as high as some other cyanobacterial species."
Blue-green algae can also appear pink
The algae has been washing ashore over the past week, and can appear pink, purple and green, and is pooling in drifts on the ebbing tide.
"Although we call it a blue-green algae, when you get a surface bloom it tends to go pink," Dr Robson said.
"Later in the year it often gets confused for coral spawn.
"That particularly bad smell is a dead giveaway that it's trichodesmium."
Blooms may be increasing
Despite its annual appearance, there is an indication the blooms may be increasing.
Dr Robson said agricultural run off may be a trigger for blooms.
"We have always had trichodesmium blooms," she said.
"There's some suggestion in the data globally that trichodesmium blooms might be starting to become more common and happening more often.
"It's not entirely clear if it's a climate change effect or due to nutrient impact from the land."
