Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: Fertilizer in runoff leads to algal blooms and dead zones in bodies of water. This type of pollution is called nonpoint-source pollution. Point-source pollution includes waste water from factories and sewage treatment plants. Hot water discharge causes thermal pollution. Answer: excess of fertilizers and other nutrients
Output:
What causes eutrophication to occur?