I was wearing heavy pacific NW dive gear.
So thick boots -- I think I just messed up and didn't have the quick release buckle in all the way or the strap was just plain too loose.
I think I just didn't pay enough attention to my fins with getting my new wetsuit all tweaked in (the attached hood was different then anything I dove in before)
So its another case of not going slow enough/careful enough and making sure I was ready to enter the water I suppose its better to learn this lesson here floating in a shallow lake then on the dive boat next weekend.
If you are diving with a buddy (hopefully), have checking your fins part of the routine. On my last shore dive, I stuck my reg in, laid on my back and had my buddy hoist my fins out of the water and check the buckles. Put your reg in though as your head will probably go under.