Hot Lake off Firehole Lake Drive.
Steady Geyser in Firehole Lake. Firehole Lake drains into Hot Lake. A swim here would be deadly.
A look back at Firehole Lake. My car is the one on the right. Draw a line back towards where I'm standing and you will see another view of Steady Geyser (now on the other side of the lake from this vantage point). It stinks here and the humidity is extremely high, which encourages a brief stay.