About 10 years ago I had to cut down about 5 willow trees that lined this fellows driveway/dam. All of the trees were about 15 to 25 feet high and the trunks where all the leaders joined together was about 18 to 24" in diameter with leader that were about 5" to 12" in diameter. All the trees were leaned way over the water and since I was working by myself I just dropped them in the lake, and then tried to pull them out with a 4x4 in low range. The lake was about 8 or 10 feet deep where the tips where at and about 4 to 6 feet where the middle section of the tree layed in the water.
I dropped the first two trees then tried to pull the out with the 4x4. They barely budged. The lateral branches dug into the mud at the bottom of the lake an acted like an anchor. So then I had to wade out there with the chainsaw and try to cut the branches that were underwater on the bottom side of the trunk, talk about a water rooster tail. Then once I got all that part done, the truck still had problems because the butt of the trunks just dug their heels into the bank of the lake.
The next few willows I climbed as high as the weak trees would let me and stripped it all down, then cut the trunk in 8' sections before dropping the bottom. It was much easier trying to drag it out of the lake when it was already cut up in sections.
As I mentioned if you don't have a real big vehicle with a real big winch, I would try to take a canoe or wade out there and use a pole saw to get the branches off. Drag the branches out first, then it would be fairly safe to walk out on it and cut it off in 8' foot sections, because if it fell then, you would be less likely to be pinned under water if the trunk is bare. It looks like the creek is low so if you cut it like it is, I bet the branches will anchor it in the mud. Anyway Good luck.