Blue Spring is the 8th largest spring in Missouri and it has the deepest blue color of any of them. The average daily flow is 87 million gallons of cool, clear water. The site is part of a seventeen acre natural conservation area and thus relatively protected. Early Native American called it the Spring of the Summer Sky. The spring is 310 feet deep and its blue color is attributed to both the depth of water and dissolved minerals. The color can vary, even during one day, depending on any storm run off or angle of sunlight hitting the surface of the water.