Fremantle tidal movements are mainly diurnal with a small semidiurnal effect evident during neap tides. Astronomical tides range from .66 to 4.6 ft (0.2 to 1.4 m). Port authorities state that the normal extreme range of astronomical tides is 3.9 ft (1.2 m). Tides are measured at five locations throughout the port area.

In the entrance channel to the Fremantle Inner Harbor, currents flowing to the south across the Inner Harbor entrance may attain a rate of 1 knot. However, there is no recorded data of current flows during the passage of a tropical cyclone. There are no significant currents in Cockburn Sound.

It was reported in the Sailing Directions for the North and West Coasts of Australia (Defense Mapping Agency, 1994b) that after a period of heavy rains, Swan River produced a strong freshet in Fremantle Harbor. This current set obliquely on to Berths 8 and 9 at about 5 knots, then parallel with the jetties, then strongly out of the harbor entrance. In the approach channel to Gage Roads, the current ran out of the harbor at about 4 or 5 knots, setting to the southwest when clear of the South Mole.

Source: http://www.nrlmry.navy.mil/port_studies/thh-nc/australi/fremantl/text/sect6.htm