I think whether a dragon can swim depends entirely on the type of dragon being imagined. If dragons were giant reptiles with powerful limbs and long tails, I don't see why many of them couldn't swim surprisingly well. Large animals often develop ways to stay buoyant or propel themselves through water, and a muscular tail could function similarly to that of crocodiles or large lizards. On the other hand, dragons portrayed with extremely heavy armor-like scales and enormous wings might struggle if their bodies weren't adapted for aquatic movement. Fantasy settings also introduce magical dragons that can ignore normal physics altogether, making the question even more interesting. Personally, I like the idea that different dragon species would have different abilities: mountain dragons might avoid deep water entirely, forest dragons could cross rivers comfortably, and sea dragons would spend most of their lives underwater. That variety makes fantasy worlds feel more believable because not every dragon has to share exactly the same strengths and weaknesses.
