People who know my Global Dinosaur Monument will may remember my Nanshiungosaurus pond [link] where I already hint this theory. I wonder why no one has imagine this yet, even Wikipedia write that all therizinosaurs were found in non-aride layers. In addition they have huge feet which are perfect to cross swamps and the long neck would be also suitalbe to grap water plants. Some modern birds have closeable nostrils... maybe a feature which is older than we think... I don't want to say here that therizinosaurs were semiaquatic; I suggest, how the title says, a livestyle which is similar to the modern moose/elk which often can be seen by grazing in the water. Another suggestion I want to make here is that therizinosaurs may carry their youngs on their back. The thorax was very wide, as far as know, and together with muscles, skin and feathers it was maybe a nice place to rest when Mum was searching for food.
Edit: I have still not much practice in painting water, so forgive me the horrible quality.