You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

Excess nitrogen fertilizers sometimes drain into waterways that flow into the Chesapeake Bay. This nitrogen may cause algae blooms, which reduce dissolved oxygen in the water. How does nitrogen negatively affect the Chesapeake Bay?
(A) fish births increase (B) fish populations decrease (C) sediment on the bottom of the bay decreases (D) the rate of water runoff into the bay increases
B