The calm, shallow waters of coastal estuaries are easily polluted by

no doubt the answer is E but isn't D a contrapositive for the cause and effect?

Sewage nutrient --> Proliferation of Algae
No Algae --> No sewage?

All answers are extreme and add new information apart from E.

Had the same doubt in mind. Unless someone gives lucid explanation, we should select the less strong answer amongst two top choices.

Dear dhineshpg
the stimulus provides info: "When estuary waters become overnutrified as a result, algae proliferate."
Conditions:
Waters become overnutrified - > Algae proliferate
OR
Algae proliferate - > Waters become overnutrified

But, stimulus does not stay that polluted by nutrient-rich sewage - > algae proliferate
The following is not a conditional statement:


Dear KarishmaB
could you check my reasoning.

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?

(A) 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. - WRONG. No such compared can be inferred.
(B) In estuary waters that contain abundant algae, microorganisms that are toxic to fish reproduce more quickly than other types of microorganisms. - WRONG. Reproduction not discussed.
(C) 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. - WRONG. No such possibilities are discussed or suggested in the passage.
(D) Algae will not proliferate in coastal estuaries that are not polluted by nutrient-rich sewage. - WRONG. Either of the red text can be either true or false.
(E) Overnutrifying estuary waters by sewage can result in the death of most of the fish in the estuary. - CORRECT.
This is as easy as it can get. However, E just reiterates the passage - it's not even a rephrase.

Answer E.

E must be true. We can map the following causal chain of events from the passage:

nutrient-rich sewage >>  pollute coastal estuaries >>  overnutrification >> lots of algae >> possibly feeds toxic microorganisms >> most of the fish in the estuary die
We can see that the possibility that (E) presents must be true, if the statements in the passage are true.


Option D is close but it not the only condition so it can be false and need not be true for this argument.