You will be given a definition of a task first, then some input of the task.
Given a scientific passage and an answer, generate a question for the given answer.

Passage: Many lakes are not natural, but are human-made. People dam a stream in a suitable spot. Water backs up behind the dam, creating a lake. These lakes are "reservoirs" ( Figure below ). Answer: resevoirs
Output:
A man made lake is known as what?