This image is a look into the depths of the Morning Glory Pool. It is one of the easiest thermal vent pools for tourists to see, but this has led to the deterioration of it’s colors.

The caption states:

3954 – Morning Glory Pool, Yellowstone National Park. This is perhaps the most noted of the dozens of beautiful hot water pools occurring in the park.

–The deep blue of the pool shown in this image is long gone. Tourists have dropped so much foreign material into the pool that it’s biome has changed, and the blue is completely gone, replaced with a pale green ringed by orange and red.

This image likely dates from the 1940s.