The objective was to determine how and to what extent the chemistry of fresh and saline waters is controlled by clay minerals and associate organic matter. Information is presented separately on Coastal Plain rivers and estuaries. Georgia Coastal Plain streams are characterized by low suspended load, low ionic strength, low pH, high PCO2, dominance of Na-Cl over the more usual Ca-HCO3-SO4, relatively high proportions of SiO2, Al, and Fe and high dissolved organic content. The streams chemistry is controlled by atmospheric input, weathering of the soils, and by organic compounds produced on decay of vegetation in swampy terrain. (Author)