Extends to the south-west from Broken Bay. It is the same name as that of the village of Cowan. Reed gives it as an Aboriginal word meaning “big water”. Halstead says that it was first recorded in 1826 when William Bean sought a land grant, and that it was officially known through most of the 19th century as"The South West Arm". It is said by Kennedy to be named after a place in Scotland. According to Jervis the name was definitely in use by 1823. A 1953 Lands Department map shows the entire creek as Cowan Water.