In Europe, they are called Divers because of their superior diving abilities. Loons are foot-propelled diving birds that are represented by four species in North Eurasia and North America. Loons were once thought to be related to Grebes, but have been found to have no relationship to any other living order of birds. They have sleek bodies wider than high for stability on the surface of the water where they spend most of their lives. Male and female loons look alike, with the only difference being that the female is smaller.
Loons have thick necks, dagger-like bills and small pointed wings.
Being a water bird, they naturally have webbed toes. Their feathers are hard and compact, except on their neck where the feathers are soft and velvety. Found in both salt and fresh water, loons are the only birds having some solid bones. Here is a site with several very nice pictures of loons. There have been tales of Loons swimming underwater for 5 minutes at a time and half a mile or so underwater.