You will get the entire gamut of responses on proper installation. For me, it's a hybrid of what I consider best practices.
Agreed with Ghostown: the vertical compressive force is critical, so an increased footprint is needed. A concrete mass on firm subsoil works well and is the cheapest....a concrete pier. Putting a fence post in a hole (elevated off the bottom with a brick or similar) and concrete poured around it is fine. Not so, IMHO, for a well designed support of significant vertical pressure (weight). I prefer to see a concrete footing, independent of the structure or post it will support. Adding some rebar vert's and 3 or 4 ties is cheap insurance, particularly if the post it is going to support may be subjected to shear forces of wind blown ice floes. The top of the concrete pier would have a stout metal bracket to link the pier to the post above. Regarding projected life of green-treat, my studies show .6 retention suitable for submersion in fresh water. I don't recall the life expectancy, but using the above mentioned method of support will allow reasonably easy repair and/or replace of a rotted timber in the future.