Why is the water red?

The St. Marys River has been mentioned in several recent articles for the Fernandina Observer — let’s add one more!

Why is the water in the St. Marys River red?

That was definitely my question when I saw my first “black” river 26 years ago. Is the water dirty? Is it safe to swim in? How did it get that way? Locals assured me that yes, the water is safe and no, it is not dirty. Blackwater rivers are known to be some of the cleanest rivers; the water is just as it's supposed to be, but what causes the coloration?

The locals explained to me that just as a tea bag of herbs steeping in a cup will change the water color, the same process is happening in the river. As rainwater flows through fallen organic debris, brownish-amber plant chemicals are extracted and filtered into the water. The decaying organic matter includes leaves, bark, roots and pine needles. This process produces tannins.

Tannins are weakly acidic and contain multiple phenol groups; they belong to a group called polyphenols. Tannins are natural chemical compounds found in plants. They are found in common foods such as red wine, dark chocolate, coffee, tea and nuts. Additionally, they are found in the oak barrels that are used to age wine.

Because of their bitter taste, plants use them as a defense mechanism to stop animals from eating unripe fruit. Tannins make your mouth feel dry and puckered when you eat them.

Tannins have traditionally been used to “tan” hides. Indigenous groups in Florida such as the Seminoles and the Miccosukee tribes used the bark extract of the bald cypress and the slash pine to cure animal skins. Settlers in early Florida steeped oak bark in water to make a “bark liquor” for preserving and softening hides. Oak trees are world-renowned for having high concentrations of tannic acid, which is used for tanning leather.

The blackwater rivers that are closest to Amelia Island include the St. Marys River, the Santa Fe River, the Withlacoochee River, and the Suwannee River. The St. Marys River and the Suwannee River originate deep within the Okefenokee Swamp, where much of the steeping occurs. The Santa Fe originates from the Santa Fe Lake near Keystone Heights, Florida, and the Withlacoochee originates from Tift County, Georgia. The water in all these rivers has been steeped in the rich organic matter that is native to southern Georgia and Florida.

The most striking contrast in color is when you are traveling on a blackwater river and find yourself at a spring. For example, where Blue Springs meets the Suwannee River, in Orange City, Florida. The contrast between the crystal clear spring water and the amber/red/brown waters of the Suwannee is something to see! It looks like blood flowing into the pristine spring waters. The color is not the only difference between these two rivers; in the summer, the Suwannee can be over 80 degrees, and the spring water is closer to 70 degrees. It is a fun visual and sensational experience to go back and forth between the two bodies of water where they meet!

Locally, you can see the coloration caused by tannins in the water when the conditions are right, just off our island — found where the Amelia River and St. Marys River meet and flow toward the Atlantic on the northern tip of Amelia Island at Fort Clinch State Park. Another place to view the tannins in the water is Little Talbot and Big Talbot Island State Parks just south of Amelia Island. The tannic water from the islands’ decaying plant matter flows off the land, seeps out under the sand, and creates red pools on the beach, again when the conditions are just right!