I visited a local park and noted the yellow gum blossoms on the ground. My friend and I speculated about whether the rainy weather might have caused it but we both agreed that it is more likely to be the outcome of cockatoo activity.
After that walk, I took our dog to Willsmere Park where the river was very muddy-looking.
I know that people have often referred to the Yarra River as the 'upside down' river and it was clear why they might say that. It looked like a path rather than water. Penny doesn't usually care, she will happily swim in it. I didn't let her swim this time though, the current was a bit too strong.
I found this quote about the quality of the water at Wikipedia.
The distinctive colour of the river is easily recognisable.
The Yarra River has been derogatively called "the river that runs upside down", a jibe at its high turbidity. The muddy brown colour is caused by the easily eroded clay soils of its catchment area. The water was clear at the time of the first European settlements, but intensive land clearing and development since the mid-19th century has resulted in the presence of microscopic clay particles. The particles are kept suspended by the turbulence in some parts of the middle and lower sections of the river. When the river water combines with marine salts as it enters Port Phillip, the suspended particles clump together and sink. The presence of clay particles is not a major factor in the pollution of the river.