Growing that close to water and being that big, I'd say willow or cottonwood.
We have 10's of thousands of ash trees here locally . All dead from Ash Borers and not one has a bump of any kind. Any burly bumps here are normally hickory or oak.
The oldest tree in the state of Maryland is an ash, it's owned by a friend of mine and is about a mile from my house. The tree is over 300 years old and has some sort of historic designation here. It got ash borers a few years ago and the state paid over $5000.00 to have it "treated". I don't know what they did for five grand, but the tree is still alive and healthy, but it has knots just like this one pictured. Not anywhere near as many, but they are there. Most are out on the smaller limbs, but there is a few on the trunk. Bark looks exactly like this one.