A body was found Saturday night in the McMillan Reservoir in Northwest Washington, authorities said.

The cause of death was not known. Police said it was difficult to determine whether any injury had occurred.

The body was found about 7 p.m. in the reservoir, which is part of the city’s water supply system. Much or all of it is surrounded by a chain link fence and it was not immediately clear how the reservoir was entered.

The reservoir lies between the Howard University campus and the MedStar Washington Hospital Center.