Here is a set of repeating frames showing a merganser chasing fish. Sometimes the birds do this for quite a few seconds at a time, and sometimes they swim for a distance underwater leaving no surface disturbance at all. The bird shows either one or two humps, both of which are composed of water.

Sometimes it is best just to publish the picture, as no amount of argument will convince some people that birds can occasionally seem to have a head, neck and two humps in the finest monster tradition. Here, one chick is following closely while another is riding on mother's back.