One of the U.S.‘s most-prized nat­ur­al attrac­tions is Yel­low­stone Nation­al Park’s Grand Pris­mat­ic Spring, the largest hot spring in the U.S. and the third-largest in the world. It’s approx­i­mate­ly 370 feet in diam­e­ter and more than 120 feet deep, but its most dis­tin­guish­ing fea­ture is its strik­ing col­oration: Its 160-degree water is a bril­liant shade of blue in the cen­ter, then it turns from yel­low to orange to red around the edges. The rain­bow col­ors are caused by dif­fer­ent bac­te­ria and heat-lov­ing algae.