Salt or freshwater Geoff.
The reason I ask is regarding water level fluctuation.
Saltwater has tide considerations.
So, a floating dock is probably best.
Winds, or current?
This will determine how much help you need to keep the dock in place out from the shore.
High winds, waves, and rough water would mean you might want a very solid anchor point on the shore - possibly concrete as you asked.
However, you can also create a simple "saddle" to mount (hinge) the dock from.
Build an "H" with 4x4 pressure treated and sink it into the ground like fence posts with some concrete around the 4x4's to hold them in place.
Fence building has a rule of thumb.
2/3 of the post above ground and 1/3 below.
However, you're anchoring a dock, not a fence post.
I would maybe look at the frost line in your area and sink the 4x4's below that with an additional 6-8" or so.
Hinge the first dock section to the crossbar of the "H".
Use heavy barn door hinges - stainless steel if possible (316 or 321 is best - especially with saltwater).
2" pipes driven into the sea/lake/river bed can be used to hold the dock in place going out from the shore.
Short sections of 2.5" pipe can be strapped to the dock sections where the 2" pipes are.
Your 2" pipes run inside the 2.5" short ones, allowing the dock to rise and fall with the water as needed.
Use pressure treated or composite so it lasts a long time.
Use stainless steel fasteners for the same reason.
Especially if it's salt water, again, 316 or 321 being the preferred stainless steel if possible.
Hope that helps.
Show us pics of it when you finish.
Good luck partner.
