The name shows on a federal government map as early as 1919. Its origin is not precisely known. In botany, “agar” refers to seaweed of various kinds, and the gelatinous substance extracted from it, which is used in food preparation and bacterial cultures. Agaric is a fungus that includes the common mushroom. Therefore, when named, there may have been an abundance of mushrooms around the lake. It is also a surname.