I think your concern about treated wood or galvanized posts in a small pond are unwarranted unless your pond is a small garden pond,and even then I personally wouldn't be concerned about them. I have both in my three small ponds, and larger pond, and never had any problems. One small pond even has trout.
How big is your pond?
At least in our area wood isn't treated with arsenic anymore.
The steps are pine which will have to be painted this year.
It doesn't get much easier than the above for a pier, and if you don't have a steep bank like this particular pond you won't even need to make steps going down to the water. It easiest to install them on the ice if you have any, but it's still possible to put them in without ice.
I've installed piers with galvanized posts and brackets from Menards this way all the way across my biggest pond, which is 130 feet across.
