Here boats travelling in opposite directions have passed quite close to each other on a perfectly calm loch. The inner pair of lines converges to the left, indicating that the boat that created it was travelling in that direction, and passed through the area viewed after the other boat, travelling to the right. The outer pair of lines converge to the right, and in the centre right of the picture the propeller wash of one boat can be seen. In various parts of the picture humps and black shapes can be seen. These are caused by interference of the two wave patterns. Standing waves, resembling black humps, appear from time to time in areas of boat wakes leading to a combination of stationary and moving black objects...a veritable menagerie of monsters for the inexperienced observer.

In the photograph below,  one arm of a boat wake shows the typical "moving humps" effect which often misleads inexperienced observers. The viewer must be outside the wake pattern  to see this effect, and the real cause of the disturbance can usually be identified by looking "further up" in the picture where first, a propellor wash can be sometimes be seen, and much further away, the other arm of the wake.