We are taught growing up that water is blue, but some rivers are black, brown, emerald blue, green, or even blue-green. So what gives these rivers their colors?
First we need to understand what color is. Natural light is actually made up of a number of different colors associated with different wave lengths within the light spectrum. Think of the multiple colors of light when refracted by a prism. The color we associate with anything is the range of light waves that is reflected back to our eyes by the molecules that comprise the entity. We don’t see the colors of light that are absorbed. When it comes to pure water, blue light is reflected while other colors of light, especially reds, are absorbed. Factors such as minerals, soil runoff and sediment, and even algae can cause water to vary from its natural color of blue.
Many Colors from Minerals
Perhaps the most common cause of water color is the presence minerals. When a rock is weathered down over time, the minerals from the rock are dissolved and small pieces are released into the water causing different colors. Iron, manganese, and calcium carbonate from limestone all common minerals that can cause water to range in color from red and orange to green and blue.
We sometimes hear from people worried about an area of their creek being orange. This is often due to iron. In groundwater that contains abundant dissolved oxygen, iron and manganese form solid mineral phases and cannot be dissolved to any extent. In some groundwater, however, there is a limited amount or no oxygen present. Under that condition, iron and manganese dissolve in the water. At a groundwater seep or spring, when this water encounters oxygen from the atmosphere, these elements precipitate as very small particles of iron hydroxide (orange) and/or manganese hydroxide black) minerals.
Color may also be affected by the concentration of natural dissolved organic acids such as tannins and lignins, which give water a tea color. These are formed when plant material is slowly broken down by organisms into very small particles that are dissolved into water. The color can also be leached from leaves, roots, and other vegetative matter.
Sediment and soil runoff can also change water’s color – sometimes as a temporary color change after storms and sometimes permanently if the river constantly carries lots of sediment. This sediment can come from river banks, but can also come from other area within the rivers drainage area such as bare ground in construction areas and farm fields. You might think "it's just soil, it's natural and so not a problem," but this is not correct. Sediment is listed as being one of the most common impairments in the Great Miami River. Sediment can carry other chemicals with it such as fertilizers and herbicides from our neighborhoods and farms. It can also bind with metals and hydrocarbons from industrial areas. Our office was instrumental in developing plans for construction sites to reduce sediment runoff. We also work closely with farmers and landowners to encourage practices such as no-till to keep fields covered.
Rainbow or iridescent Sheen
Everyone's first thought is an oil spill, but that's not always true. A non-petroleum sheen can usually be distinguished from a petroleum sheen by attempting to break up the sheen. When a stick is poked in to a bacterial sheen or a stone is dropped in to it, the sheen will typically break into small platelets. In contrast, a petroleum sheen will quickly try to reform after any disturbance.
Algal blooms are natural occurring over growths of algae caused by sunlight, slow water, or excess nutrients. Pollution runoff from humans can also increase nutrients in the water and cause an algal bloom. Algae affect not only the health of a river but also the color. The color caused by algae can vary from a dark green to almost a reddish color. Algae consume nutrients from the water along with dissolved oxygen causing negative effects on the ecosystem of the river. Once the algae begin decaying it releases methane gas causing foul odors. This algae decay can also severely reduce oxygen levels in the water causing problems for aquatic life.
White cloudy or milky water with no identifiable solids, suds or odor is likely runoff from paint, cement materials or washing equipment.
Gray & Smelly
Gray discolored water with a strong sewage odor indicates a possible sewage overflow.
White sudsy water is usually associated with car washing, pressure-washing or other detergent discharge.
What's the problem
Even when the color comes from a natural source, generally colored water imparts adverse effect on human health and aquatic environment. As pure water doesn’t possess any kind of color, a waters color may provide evidence that there is some form of contamination. All kind of particles- organic matter, algae, sediments, dissolved minerals or other artificial chemicals are harmful to human and aquatic health.
Highly colored water has significant effects on aquatic plants and algal growth. Light is very critical for the growth of aquatic plants and colored water can limit the penetration of light. Thus highly a colored body of water could not sustain aquatic life which could lead to the long term impairment of the ecosystem.
If you think you have pollution in your creek, you can report it to Bob Lentz at the Butler County Storm Water District, email, or 513-785-4101. You can visit their website at www.stormwaterdistrict.org.