The text reads: “Where the Mississippi River meets the Gulf: not mixing ever with one another.” The meme has been shared almost 50,000 times.
It shows water from the Mississippi River flowing into the Gulf of Mexico, south of the US state of Louisiana. The photo comes from a YouTube video posted on 13 November 2015 by offshore fishing magazine the Marlin.
Is it true that the waters of the Mississippi River and the Gulf of Mexico never mix?
Fresh river water distinct from ocean water
Africa Check asked the International Society of Limnology, a global body for researchers studying lakes and inland waters, about the claim via their Facebook page.
The society’s Prof Yves Prairie, the Unesco chair in global environmental change, responded.
“No, the claim is not true,” he said in a direct message on Facebook.
“The waters eventually mix but when two waterfronts of different density (salinity) and colours meet, they can remain separate and look like that for quite a while. They will eventually mix, and probably at depth so you might not see it at the surface.”
According to the US Environmental Protection Agency, as “nutrient-laden water from the Mississippi flows into the Gulf, this freshwater is less dense and remains above the denser saline seawater”. The freshwater is also warmer than the deeper ocean water, “further contributing to the stratification”.
River water eventually causes ‘dead zone’ in the ocean
The caption to a similar photo published by Marlin magazine on 22 July 2014 says: “The Mississippi River and Gulf of Mexico come together to form a ‘dead zone’, where the difference in colours is noticeable.”
The US National Oceanic and Atmosphere Administration (Noaa) explains the cause of the dead zone, an “area of low to no oxygen that can kill fish and other marine life”.
Each spring, it says, fertiliser used on farmland is washed by rain into streams and rivers, and flows into the ocean. Here the nutrients in the fertiliser “stimulate an overgrowth of algae” – known as an “algal bloom”. Algal blooms do occur naturally, but are also caused by human behaviour.
The overgrown algae eventually die, sink and decompose in the water.
“The resulting low oxygen levels near the bottom are insufficient to support most marine life and have long-term impacts to living marine resources that are unable to leave the area,” Noaa says.
The photo circulating on Facebook is of the Mississippi River flowing into the Gulf of Mexico, but the phenomenon can be scientifically explained.
Fact-checking organisation Observers of France 24 checked a similar claim on distinct ocean waters and concluded that “it’s not true to say that the two bodies of water aren’t mixing”.
Fact-checking site Snopes also investigated the photo of the Mississippi River flowing into the Gulf of Mexico and says the “two distinct colours in the photograph are not… a permanent fixture along the border of different bodies of water”. – Grace Gichuhi
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