The Swan River in Perth is expected to peak at 1.6 metres early on Sunday as the runoff from the flooded Wheatbelt region reaches the city.
Torrential rain swelled rivers and washed away roads across WA on Saturday, with the state's Wheatbelt and Goldfields hardest hit, while Perth received its second highest rainfall on record on Friday, with more than 114mm raining down on the city.
A severe weather warning, however, has now been cancelled for the Great Southern region.
Flood water enveloped the Phillip River Bridge on the South Coastal Highway near Ravensthorpe on Saturday afternoon, leaving 15 people from six vehicles stranded.
WA's Fire and Emergency Services said they contracted a private pilot of a small helicopter to rescue a group.
Flooding hit the community of Toodyay, along Stirling Terrace, and Mortlock River East at O'Driscolls Farm.
Water levels within the Avon River catchment were expected rise over the weekend and moderate flooding was also expected along the river in Beverley.
