Provided by WebExhibits.org, the Why is Water Blue? (1) Web site starts off this Topic in Depth. Visitors will learn the factors that affect the colors we see, what color water actually is, and the basic physics and chemistry behind the phenomenon. This site is hard to beat for its clear explanations as well as its interesting photographs and illustrations. The second site, entitled the Common Water Quality Complaints Color Guide (2), gives possible sources of nineteen color variations in water. For example, if water is reddish-orange, it most likely contains high iron concentrations. This unique and useful site is brought to the Web by the University of Colorado Boulder department of Geography. Next, from the Smithsonian Environmental Research Center, comes the What is Hydrologic Optics? (3) Web site. Explanations of water optics including scatter, attenuation, and absorption are given along with waters inherent and apparent optical properties. The fourth site, Water Color (4), is provided by Annis Water Resources Institute of Grand Valley State University. The page describes the Forel-Ule color scale, which provides a standard method for determining water color and tells why a waters color is significant. Next, from NASA's Visible Earth Web site, the Ocean Color (5) page gives a unique look at the color of oceans from around the world. The seven impressive satellite images, which include the Mississippi Delta and the Black Sea, include explanations of what is most likely causing the color differences. Anyone who has ever visited Yellowstone National Park knows that the brilliant colors of the many mineral springs are breathtaking. The sixth site, from the National Park Service, highlights one of these called Emerald Spring (6). The page describes how sulfur combines with reflected blue light, which makes the hot spring appear a magnificent emerald green. Next, the Laboratory Services (7) page of the Michigan Water Research Center Web site explores several physical measurements of water including color. The page contains a description, along with various links, regarding what substances cause the color of water to change and what is meant by true and apparent color. The last Web site, Secondary Drinking Water Regulations: Guidance for Nuisance Chemicals (8), is provided by the US Environmental Protection Agency. The site describes what secondary regulations are, why color is one, and what the standards are for color.