How can you walk the thing in water without getting the wheels wet? The two sentences seem like a contradiction.

It only has two wheels... You walk it blade first towards the pond, all the way until the wheels are at the water's edge. The cutting blades are well out into the water cutting whatever you want them to be cutting. You back it up, then move over and walk it back to the water's edge... You keep repeating the process. It is a pain because you can only mow a deck width at a time, but it does work.
Like I said in my other post, the thing is awesome. 3 years, no issues and still cuts through just about anything 1" and less in diameter. I have driven it over 2" black locust and it'll even blast through it.