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Why can swamp water appear yellow, brown, or nearly black?

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Bald cypress trees with wide, flared trunks stand in still, shallow water in a Louisiana swamp, their green foliage creating a dense canopy. — Wetland Stately bald cypresses (*Taxodium distichum*) thriving in a Louisiana swamp.

Swamp water often appears yellow, brown, or nearly black due to the incomplete decay of organic matter in the wetland ecosystem.1

In these environments, slow water movement and a lack of turbulence result in low oxygen levels. Because the decay of dead vegetation consumes available oxygen, the decomposition process is often incomplete. This leads to an accumulation of resistant organic substances, specifically humates and tannins, in the substratum. The presence of these compounds gives the water its characteristic coloration, which can range from yellow to a deep brown that resembles strong tea or coffee.1