Imagine that after hiking for days in a remote area where y…

Imagine that after hiking for days in a remote area where you are completely alone, you find the most beautiful valley with the most beautiful river running through it. You rip of your clothes smiling in anticipation of refreshing yourself in the beautiful cristaline water. You wade in and then suddenly you see it and freeze:

A sign half consumed by rust with a symbol you know very well saying RADIATION HAZARD. DON'T TOUCH THE WATER

Describe the change happening in your mind after seeing the sign.