As long as it's not cut from the bank I think you're ok. I know a guy got caught on degray a few years ago cutting brush off the bank. That's a big no no. He had to plant a lot of new trees on top of his fines what I heard. But, do the right thing and check the book! If it says it's ok, take the book with you. Some game wardens like to try to make people that don't fully understand the law feel like they are breaking the law and stick you with a ticket. It's happened more than once.
The good thing about sinking your own as you will have your own honey hole until others find it. Christmas trees shouldn't be too hard to put out. I cut a couple of 20 foot cedars that were 8 feet in diameter. My 25 horse really struggled to drag them on a windy day. We had to come back on a calm day and it took an amazing amount of weight to sink them. This was done on private land.