Why is Tybee Island’s water brown?

SAVANNAH, Ga. (WSAV) – When you think about beaches, bright, crystal blue waters probably come to mind, so why is the water on Tybee Island’s coast brown?

When it comes to the brown water on Tybee Island, geology and the nature around Tybee both play a huge part. The naturally occurring chemical compounds, known as tannins, are the main culprit.

Tannins, also called polyphenols, are naturally occurring plant compounds. Tannins, mainly from decaying marsh grass, leach into Tybee’s beaches due to the salt marshes and tidal rivers along the Tybee coast.

Though it makes the water less appealing for many, brown water doesn’t mean that the presence of tannins in the water indicates contamination or pollution. It benefits our marine ecosystems by providing shelter and food sources for organisms like fish, crabs and shrimp.

Along with that, the salt marshes surrounding Tybee Island help work as a natural filter for water and provide homes for our plant and animal life which helps to sustain our coastal ecosystem.

The brown water also helps maintain a balanced ecosystem by supporting the growth of phytoplankton, which is the foundation of the food chain for marine life and helps support larger animals like dolphins and sea turtles which are two of Tybee’s staple marine life.

To add to the general tannins from Tybee’s marshes, runoff after storms and rainfall adds more sediment and organic matter to accompany the tannins in the water.

The ocean currents around Tybee Island also contribute to the color of the water since they mix with the tannic water. This means that the color can come off more blue, brown, or even a yellowish tint depending on tides and currents off the coast.

Though the brown color can be very unpleasant compared to other beaches, the water quality is not at risk due to tannins. Water quality on Tybee’s beaches is monitored and tested by the Chatham County Health Department (CCHD) for enterococcus bacteria weekly, according to their website.

Enterococci are bacteria that live in the intestinal tracts of warm-blooded animals like dolphins, birds and humans, which can indicate possible contamination of streams and rivers by fecal waste, according to the Environmental Protection Agency (EPA). Enterococci can make people sick, but if the CCHD finds that the level of bacteria present is above the EPA’s recommended standards, the beach will be placed under advisory.

Some of the sources of fecal bacteria like enterococci include wastewater treatment plant effluent, leaking septic systems, domestic animal and wildlife waste, stormwater runoff and sewage discharged or dumped from recreational boats. There are also natural, non-fecal sources of fecal indicator bacteria, including plants, sand, soil and sediments which can contribute to a certain background level in ambient waters, the EPA said.

To recap, Tybee’s beaches are not brown due to pollution or being plain dirty, but dense with tannins which helps keep our coastal ecosystem healthy.