they seem too big to weirdly shaped trees and too sticking out of the ground to be holes
Look like ponds to me. Though I’m sure there’s a technical term for them.
In fact, if you drag the “little man” usually used for street view, you’ll see there’s a couple of pics of them from ground level.
They look as though they are convex because the illumination is coming from below (the south, but more importantly, towards the bottom of your screen). It is a variant of the hollow face illusion.
You can also see that they are pools if you switch to map view.
Correction: Not the hollow face illusion, which is a related thing, but not quite the same.
The actual illusion in question may not have a catchy name, but it is a well recognized effect that arises from the way the visual system derives shape from shading. However, how I originally described it is correct: Other things being equal, the brain tends to assume that a picture represents a scene as lit from above. If it is in fact lit from below, this can make what are actually concave hollows appear as convexities (or vice-versa). There also seems to be a bias toward seeing things as convex rather than concave if there are no clear cues to concavity. See this article (large PDF from Scientific American) and this one (more recent scientific journal article).
The human brain strongly identifies shadows and corrects the perceived image from that.
The fake shadows appear on the lagoons due to the wind, the windward edge has no ripples, hence appears dark. The silvering is being created by wind creating windows.
You can see this in the “google earth” and “historical imagery”, pictures from different days…
What makes you think it is wind and waves, rather than the direction of the lighting, as I said? In fact, all the pictures taken at ground level show the surface of these lagoons as dead calm and flat. They are not very large, so are not likely to develop very significant waves even in high winds. On the other hand, they are ringed by vegetation, quite sufficient for casting shadows (real ones, not fake ones) when the sun is relatively low in the sky. Shadows of that type are quite sufficient for creating the illusion of convexity (see my links).
The “historical” images differ from one another because they were taken at different times of day, with the sun in different positions in the sky. There is no indication that they were taken under different wind conditions. Furthermore, waves in the nearby sea are clearly visible as such, whereas none are visible as such on the lagoons.
I suppose some of the mottling effect in the original image may possibly be due to small waves created by high winds, but I see no reason to believe that this is a major contributory factor towards the illusion of convexity, and even any visual effects involving waves will also depend on the direction from which the waves are being illuminated.
“Amy” and “Rory”
I think you can clearly see from the shadows that the trees are casting that the illumination comes from “below” (the direction of the bottom edge of the screen). However, I think you can also see that the angle is pretty steep; taller trees only cast very short shadows. There is nothing high enough to cast shadows far into the lagoons, which themselves are perfectly flat and horizontal of course. I think it has to be wind. Other photos might not be taken under windy conditions.
d’oh, how could I forget about the little google maps man and his geotagged photos?
Although the illusion is very strong here, with the dark streaks looking almost exactly like shadows something standing or bending up would make (like the ‘highlights’ imply)
Yep, lagoons and tidal basins.