Water Corporation staff recently came across an unexpected find when they were working on a project in Quindalup.
The team found a whale bone which could thousands of years old.
The bone was found buried at a depth of over four metres on Geographe Bay Road during the drilling of a manhole as part of Water Corporation's Infill Sewerage Program.
Water Corporation Assets Delivery General Manager Nathan Hardwick said as soon as the crew realised what they had found, work was stopped and experts from the Western Australian Museum were contacted for advice.
"It's not every day you make such an interesting discovery when working on one of our projects, and everyone was pretty excited to find something so unexpected," Mr Hardwick said.
"We have now handed over the whale bone to the WA Museum to clean and restore so it can be accessioned into its collection."
WA Museum Earth and Planetary Sciences Head of Department Mikael Siversson said the Museum only had a few subfossil whale bone specimens and this one appeared to be a partial rib.
"The soft sand in which the bone was found, its comparatively light weight and lack of cemented shell fragments indicate the rib originates from the Holocene period, which is the current geological age, and began about 11,600 years ago," Dr Siversson said.
The bone will be in the museum's freezer for about three weeks before it's cleaned and examined.