Juvenile Pied-billed Grebe, Fernhill Wetlands, Forest Grove, Oregon on 13 July 2010 by Greg Gillson.
Two weeks ago I observed this juvenile Pied-billed Grebe at the local wetlands. To submerge, grebes either lunge forward and dive head-first, or simply sink. This bird used this latter method.
It actually happens quite quickly. The bird starts submerging at the breast, then the body goes under, and finally the head. Here are two submerging sequences.
Here's another set...