The beloved Yarra River is the centrepiece of Melbourne, dividing the north from the south, and flowing 242 kilometres from its source in the Yarra Ranges National Park all the way to Port Phillip Bay. In the city, it provides picturesque skyline views and waterfront dining, and further out into the northeast ‘burbs, you can even go for a dip in its waters. What’s not to love?
Well, there is one peculiarity about the river that does detract a little from its charm. That’s the matter of its colour, which isn’t exactly the prettiest sight. If you’re like us, you’ve probably wondered: why is the Yarra River so brown?
We decided to get to the bottom of this question. Time Out Melbourne spoke to professor Vincent Pettigrove from RMIT University, who specialises in aquatic pollution, for some answers.
The first assumption anyone would make is that the Yarra is brown in colour because of super high pollution levels in the water. But, as Pettigrove explained, this isn’t actually the real reason. In fact, the colour comes from Silurian sand particles, which are essentially clay silt that float in the top layer of the water. Underneath this top layer of the river around the bay area in the CBD, there is clear saltwater. Colour us surprised!
“You only need a tiny amount of this clay for the Yarra to look muddy,” says Pettigrove. “The saltwater is dense and freshwater floats on top, so what you see is just a little layer of fresh water going down the river, but underneath it's all clean marine water.”
This explains the appearances of the famed Salvatore the seal, who was cited as far up the river as Abbotsford, delighting Melburnians with his playful antics.
But if it’s not pollution that causes the colour, was the Yarra always such a muddy shade of brown? Well, according to Pettigrove, this is a hotly debated topic.
“One of the biggest debates that we've had is whether the Yarra was naturally muddy before European settlement,” he says. “John Batman said it was clear in his notes, and there were a whole lot of different types of fish and even sharks there.
“In Melbourne, as we're growing with more urban development and disturbing the soil with new housing developments, you don't need a lot of that to get into the river to cause the muddiness. The more urbanisation we get, the worse it gets.”
But even though the Yarra’s brown colour isn’t ideal, we should be thankful for Melbourne’s high-quality water supply these days, because if you lived here 100 years ago, the situation was dire. Back then, the main problem was that the old sewerage systems used to leak into the water supply. Yuck.
“In the early days, it was really bad… there was cholera coming from the Yarra because we couldn't separate faecal pollution from drinking water,” says Pettigrove.
Nowadays we (luckily) have multiple bountiful reservoirs from which our drinking water freely flows and poop in our drinking water is a long-gone concern. So pollution isn’t the cause of the brown colour, but that doesn’t mean the Yarra isn’t polluted at all. These days, the main issue is industrial pollution and ‘diffuse’ pollution.
Diffuse solution is the residue of chemicals from things like buildings and cars (particularly zinc, which is used in car tyres). The biggest problem for pollution in the river is pesticides, which can be anything from weed spray or products used in construction. All of these chemicals wash into our waterways and cause pollution.
But if you travel further upstream, the water quality improves and the river is even safe for swimming, especially in suburbs like Warrandyte and Warburton. But Pettigrove suggests that once you’re south of Templestowe, it’s not a good idea to take a dip. Also, it’s illegal to swim in the Yarra south of Abbotsford.
But even when swimming in the cleaner areas, it’s certainly not pristine, as Pettigrove explains.
“The biggest source of danger to humans swimming is human faecal pollution… but 99.99 per cent [of sewerage] is going into the sewage treatment plants and that gets rid of all those really nasty diseases,” he says. “(But) imagine how many dogs are walked around Melbourne and how much poo they produce.”
Ah, lovely. Swimming in dog poop. According to Pettigrove though, it’s not much of an issue in summer when rainfall is lower. He explains that the worst time to swim in the river, by far, is in the days after heavy rainfall.
“If you go out there the day after a storm, it's dangerous,” he says. “There could be bits of logs coming down the river, it's going to be muddy, and it will have more water coming off the catchments where there's dog poo, horse poo, cattle poo, whatever coming in.”
So, our beloved Yarra is a bit muddy and a bit stinky. The question is, how can we improve it?
“There's not going to be a magical thing in Melbourne that’s going to make the Yarra clean,” says Pettigrove. “The key thing is not to have buildings shadowing the Yarra… there have been some down at Southbank that have been built right next to the river and they keep it pretty much in darkness all the time.
“That's not a great thing for the river and it's not good for fish moving through it. Keeping that open space as much as we can in Melbourne is important.”
Well, there you have it. No matter what colour she is, we’ll still love our Yarra River. It may not be perfect, but we couldn’t imagine our city without it.
Stay in the loop: sign up for our free Time Out Melbourne newsletter for more city news, straight to your inbox.