Passage Summary: Fertilizer in the water causes a chain reaction where tiny plants grow and die, leading to bacteria sucking all the oxygen out of the ocean and killing the fish.

Reasoning: Agricultural runoff increases phosphorus, which boosts plankton growth; when that plankton dies and decays, bacteria consume the oxygen in the water, leading to fish death.

Analysis: This stimulus presents a clear causal chain where one environmental event triggers the next. In a 'Must be True' scenario, you are looking for a statement that is a direct consequence of these combined facts. The most reliable inference will likely connect the beginning of the chain (phosphorus/runoff) to the end of the chain (oxygen depletion/fish survival). Avoid any answer choices that suggest these events 'always' happen or that introduce outside factors not mentioned in the text.