It may look like a stunning rainbow of colour , but the psychedelic hue of this hot spring in Yellowstone National Park , is a result of years of unintended vandalism by visitors . Once a brilliant shade of blue , the Morning Glory pool 's appearance has altered dramatically since the 1950s , thanks to an accumulation of coins , rubbish and natural debris . The pool has been dubbed the Fading Glory , due to the transformation from its original colour to the yellowy-green hue it has today . Scroll down for video . Morning Glory in the Yellowstone National Park was once a brilliant shade of blue , but now owes its yellow tinge to debris and coins thrown in over the years . The Morning Glory hot spring in 1940 . The photograph reveals a stark contrast to the fiery colours now exhibited at the tourist attraction . The popular tourist attraction sees three million visitors flock to gaze at its psychedelic waters in Wyoming , USA . The site first gained popularity in the 1940s when a million tourists would visit the site . Pool on fire ! The fierce colours are influenced by how light interacts with the water ’ s depth , with yellow and orange colours in the shallows and green in the deep waters . The rainbow hot spring has been clogged up with debris , which block the heat vents , and affecting the water circulation in the pool . It is estimated that the destruction of the hot spring has been building up for decades . Research by Montana State University and Brandenburg University of Applied Sciences in Germany helped to create a model that could depict the hot spring 's colours from over a century ago , when it was less frequented by visitors . Now nearly three million tourists flock to Yellowstone National Park , compared to the one million in the 1940s , which has led to the build-up of debris in the pool . As the underwater vents started to get clogged up , water circulation was affected , decreasing the temperature of the waters and causing a migration of the orange-coloured bacteria towards the centre . Adam Hoffman from Science Friday said : 'Pigments produced by swaths of those microbes—called microbial mats—are responsible , at least in part , for the brilliant yellows , greens , and oranges that now tinge Morning Glory and other thermal pools in Yellowstone . ' Photographs from 1966 show the Upper Geyser Basin pool 's original blue colour , before the build up of coins and rubbish . The pool received its name in 1883 from Mrs McGowan , who was the wife of Assistant Park Superintendent , Charles McGowan . As a nod to its then crystal blue colour , she named it after the blue flower , Morning Glory . Although it was originally known by its Latin name , Convolutus , by 1889 it was commonly known by its current name . Over three million people enjoy the Yellowstone National Park annually , spans an area of 3,468.4 square miles , comprising lakes , canyons , rivers and mountain ranges . Unless some subterranean shift happens where more hot water can again flow to the surface , Morning Glory will never be fully blue again . Half of the world 's geothermal features are in Yellowstone National Park , fueled by Yellowstone Caldera , the largest supervolcano on the continent . The pool has warning signs around it , in an attempt to reduce further vandalism to its waters , ( left ) . It has been dubbed Fading Glory , now bearing little resemblance to the bright blue flowers which gave it its name , ( right )
Morning Glory in Yellowstone National Park has drastically changed from crystal blue to a yellowy-green hue . Debris has blocked underwater vents , causing a rise in the spring temperature . million people visit the park , and due to the rubbish and coins , it is now nicknamed Fading Glory .