Among the cow pastures and citrus groves of Florida's heartland north of Lake Okeechobee, patches of wetlands serve as kidneys for the Everglades.
"It filters out all of the impurities, in this case we're talking about nutrients, phosphorous in particular," says Ernie Marks of the South Florida Water Management District.
Marks steps through the grass framing the expanse of reeds and rushes. The vegetation sieves from the water the nutrient responsible for toxic algae blooms. Wading birds like egrets flap among the cabbage palms.