Colloquially speaking, “swimmers” are puppies that have developed a flat chest and sternum. Without therapy (which we’ve found can be as simple as really thick padding in the whelping box), these puppies (found in any breed or mixed breed) are unable to stand or crawl without aid. Fellow Puli owner, Dr. Mary Wakeman, has written about it here.
For our purposes, however, this post about swimmers refers to “water dogs” classified as such. This includes the Newfoundland, retrievers, Standard Poodle, and the American Water Spaniel. While most breeds hold themselves somewhat vertically in water, the aforementioned breeds actually position themselves differently by “laying out” more horizontally to the water surface. They even move through water differently by extending and folding their legs during the forward and backward strokes. The leg extends full length on the backward stroke and then shortens by folding the joints on the forward stroke. These dogs glide through water as opposed to “vertical swimmers” (especially those that are poorly built) which tend to splash about).
“Sadie Has A Ball” by Molly A Poole