There’s sulfur in this hot spring.
Sulfur that's yellow is still sulfur. It smells like rotten eggs, which are also kinda yellow.
The reading for this word is an exception. Here's a mnemonic to help you remember it:
This sulfur smells like an eagle's OOHHH (いおう)!! Oh no. Sulfur smells... it smells... like an eagle's... OH.. Oh eww no.