Due to the restriction of the tidal range within Port Phillip caused by the relatively narrow entrance the tidal stream near the Heads does not turn at high and low water. The force of the tidal steams depends upon the relative water levels inside and outside Port Phillip. The greatest differences in levels occur at about the time of high and low water in the Entrance when the streams run at their strongest, up to 6 knots under normal conditions and approaching 9 knots in extreme conditions.
Slack water occurs at about 3 hours before and after high water, when the levels inside and outside are the same. The ingoing stream runs from about 3 hours before to about 3 hours after high water and the outgoing stream at other times.
The main body of the ingoing stream from the southward and eastward sets at about 38 degrees directly through the entrance fairway, with drifts of considerable force across and through the reefs, spreading towards Shortland Bluff (Queenscliff) and the southern shore; thence directly through the channels of the Great Sand Bar. The outgoing stream coming directly from the Great Sand Bar channels sets towards Lonsdale Bight, and from there out through the Entrance with great force partly athwart the channel at 200 degrees thence away south eastward along the land towards Cape Schanck.
The water level and hence tidal streams can be significantly affected by barometric pressure and the direction and duration of the winds. West to south west winds cause a rise in sea level outside Port Phillip and a consequent increase both in rate and duration of the ingoing steam will continue till sea levels inside and outside have reached equality, then the increased ingoing stream will cease and the streams become normal. On the winds ceasing, sea level outside falls to normal, causing the outgoing stream to increase both in duration and in rate until sea level in Port Phillip has fallen to normal and the levels outside and inside are again equal.