Re #128:
I wonder if the sharp demarcation between silted and clear water that Paul has observed occurs along the line seen in the chart above. The darker blue area extending out from the beach is a shallow shelf which drops off abruptly where the dredger maintains deep water for large vessels anchoring or transiting across the bay.
In the couple of hours leading up to high water there is a strong tidal stream hurtling along outside the harbour walls. The harbour has to fill up to rise to the same level leading to the notorious jetstreams which pour through both entrances. These create very strong circulatory currents inside the harbour.
My theory is that there is silt suspended in the water over the shallow shelf and that the large body of water circulating in the deep section of the outer harbour is carrying away the suspended silt at the interface where they meet.
The line marking the edge of the shelf runs from the East buoy to the West buoy so if the demarcation line between silt and clear water that Paul has observed runs between these two buoys then this would corroborate my theory, probably a load of old rubbish.