Coastal sea level at Fremantle, Western Australia is strongly influenced by trade wind variations in the tropical Pacific, due to the existence of equatorial and coastal wave guides. Corroborated with low-pass filtered Southern Oscillation Index (SOI-M), Pacific Decadal Oscillation (PDO) causes high Fremantle sea levels during positive SOI-M regimes (with more frequent La Niña events) and low sea levels during negative SOI-M regimes (with more frequent El Niño events), due to enhanced and slackened trade winds. The multidecadal variation of the Fremantle sea level obscures its long-term rising trend during the 1950's to mid 1990's. Statistical regression models are used to describe relationships between the multidecadal sea level variation and SOI-M, in an attempt to separate natural climate variability and climate change effects. A non-parametric regression model reveals a nonlinear relationship, likely due to different responses of the sea level (upper-ocean) to the El Niño and La Niña events.