Residents feared it could have been some kind of industrial pollution, scientists speculated it could have been insect droppings, but it took an environmental scientist from the Australian Nuclear Science and Technology Organisation, Dr Kate Harle, to prove it was pollen.
"As soon as I saw the yellow spots on my car, I knew it was pollen, but I had to take some samples to make sure," she said.
Reports were coming in from around Sydney about the mysterious yellow goo that was spotting the landscape, and aggravating car owners.
ANSTOs Dr Harle, an expert in identifying pollen, collected some samples and put them under the microscope. They turned out to consist mainly of pollen from Xanthorrea, the distinctive native Australian grass tree.
"Bees are transporting the pollen and it is falling off their legs. Xanthorrea is common throughout the Sydney basin, so anyone living close to bees and grass trees is likely to find the yellow spots," Dr Harle said. "The spots indicate that this has been an exceptional time for the flowering of grass trees. The reasons for this could be the unusual climatic conditions, including a long late summer.
Its also believed that Xanthorrea may be stimulated to flower in the season following exposure to smoke or fire," she said.