The calm, shallow waters of coastal estuaries are easily polluted by nutrient-rich sewage. When estuary waters become overnutrified as a result, algae proliferate. The abundant algae, in turn, sometimes provide a rich food source for microorganisms that are toxic to fish, thereby killing most of the fish in the estuary. Which one of the following can be properly inferred from the information above? ['Overnutrifying estuary waters by sewage can result in the death of most of the fish in the estuary.', 'In estuary waters that contain abundant algae, microorganisms that are toxic to fish reproduce more quickly than other types of microorganisms.', 'Fish in an estuary that has been polluted by sewage are generally more likely to die from pollution than are fish in an estuary that has been polluted in some other way.', 'Nutrients and other components of sewage do not harm fish in coastal estuaries in any way other than through the resulting proliferation of toxic microorganisms.']