So can you even swim in Yellowstone? The short answer is yes. The long answer is: it's pretty limited. Although there are many rivers, lakes, and springs in the park, it's very important to note that the vast majority of the waters are incredibly dangerous.
The water in Yellowstone looks pristine and clear, but don't be fooled to think that it is clean and safe to drink on it's own. Because of the park's immense wildlife populations, there are animals constantly drinking, defecating and dying in and around these waters.
However, Yellowstone is also an active geothermal area with hot springs emerging at ~92°C (~198°F) (the boiling point of water at Yellowstone's mean altitude) and steam vents reported as high as 135°C (275°F).
As pressure is released, gases dissolved in the magma come out of solution, turning the magma into a boiling froth. The total energy released would be equivalent to an 875,000 megaton explosion. The shockwave would kill 90,000 people. Most of the lava would fall back into the crater.
This giant is the “supervolcano” that lies beneath Yellowstone National Park, the wildlife and forest preserve positioned on a sprawling expanse that extends through the states of Wyoming, Idaho, and Montana.