A north-easter drags the top of the bay towards the corner

Wind pushes the top layer of the water along with it. Anything floating goes too, so on a north-easterly day loose weed and foam end up against the wall at the South Steyne corner.

Illustration

The wind drags the surface at roughly 3% of its own speed: a 20 km/h north-easter moves the top of the water about 10 m a minute. Not to scale.