Fallout Wiki
Fallout Wiki

The Poseidon reservoir is a location in the Commonwealth in 2287.


Prior to the Great War, the Poseidon reservoir distributed water to the surrounding farmlands and towns in addition to generating hydroelectric power for use in Poseidon Energy research facilities scattered throughout the Commonwealth.[1] Since the war, the facility has fallen into disrepair.


Upon entering the facility, the maintenance office is located on the right in a metal pod, inside the office are a terminal that unlocks the security doors, and an armor workbench. On top of the office, there's a hidden toolbox, accessible via a footbridge. Past the office, a stairwell can be used to access the lower level of the facility, the lower level consists only of a room containing a weapons workbench and some containers. In the southeast part of the facility and behind a security door, a glowing one guards a steamer trunk, a chemistry station and a Master-locked safe.

The roof can only be reached via a stairwell located on the north side of the facility. On the roof, a large metal pod with an armor workbench is located upon reaching the roof. On the east side of the facility, another reservoir can be reached via a footbridge.

Notable loot

  • Robot model kit parts - On a metal table just outside the factory, in a Railroad stash (indicated by the railsign) via a large brown outlet pipe going into the lake on the south side. The area can be accessed via an underwater breach in the pipe, near the lake's edge. Enter the pipe and continue walking up.
  • Poseidon Reservoir safe key - Inside, next to a tool case behind a large pipe in the upper west section corner. Drop down from the catwalk above to reach it. Opens the safe in the room behind the security doors and the tool case right next to the key.
  • Poseidon radar transmitter - In the steamer trunk behind the terminal-gated door in the lower level, optionally used for the quest Last Voyage of the U.S.S. Constitution. It will remain stuck in inventory if the player character chooses to jury rig the guidance radar, whether or not the quest has already been completed when collected.

Related quests


The security doors remain open when the area resets.


The Poseidon reservoir appears only in Fallout 4.


PCPC Playstation 4Playstation 4 Xbox OneXbox One If traveling with Ada as a companion, upon entering the flooded basement room, she will remark "Exercise caution, ma'am. The water may be irradiated" even if the player is male.



  1. Fallout 4 Vault Dweller's Survival Guide Collector's Edition pp. 353-354: "[5.01] POSEIDON RESERVOIR
    Poseidon Energy Reservoir not only distributed water to the surrounding farmlands and towns, but it was also a source of hydroelectric power. The power generated was used by Poseidon for its research facilities scattered about the Commonwealth. Currently, the reservoir is in a state of disrepair. The hydroelectric generators no longer operate and the water has become stagnant."
    (Fallout 4 Vault Dweller's Survival Guide Map)