Waves are an important topic. Here straight lines of waves were approaching the harbour entrance. They are called plane waves. Diffraction is when waves bend when they go through a narrow gap. You can just about tell that this has happened in the bottom picture. For diffraction to be really pronounced, the wavelength must be equal to the size of the gap. Here the waves were maybe 1 metre apart but the harbour entrance was at least 20 metres across. Hence diffraction was not that good.
