From an article in 2004....
Town Doesn't Mind Brown Water
Greenville's water comes from the Cockfield aquifer, which is fed from eastern Mississippi. The water filters through three ancient cypress swamps, picking up particles from wood and vegetation thousands of years old, Jones said. The particles are dissolved in the water, giving it a brown color. Most other cities in the Southeast that receive fresh water from the aquifer have installed filtration systems that make the water clear.
Obama campaigned there and promised to remember them (the delta, and not just on the water). Do some Googling to read if he helped. I'll give you three guesses but you might only need one.