Can a swamp clean dirty water?

The Answer

A wetland is nature's water treatment plant, and its secret weapon is slowness. When dirty water spreads out into a broad, shallow, plant-choked swamp, it slows almost to a standstill, and that gives three cleaning processes time to work.

First, heavy dirt and sediment simply sink and settle into the mud instead of being carried onward. Second, the dense roots of reeds and rushes soak up dissolved nutrients like nitrogen and phosphorus, the very things that would otherwise cause algae to choke a river downstream. Third, and most importantly, the mud teems with microbes that eat and break down organic waste and pollutants, using them as food.

Fast-moving water gives none of these a chance. A wetland works precisely because it holds the water still long enough for gravity, plants and microbes to do their jobs. Protecting swamps, it turns out, protects the water everyone downstream depends on.

The principle: Wetland filtration. By slowing water, wetlands let sediment settle, plants absorb nutrients, and microbes break down waste, cleaning water naturally.