Prior to the Great War, Poseidon Reservoir distributed water to the surrounding farmlands and towns in addition to generating hydroelectric power for use in Poseidon's research facilities scattered throughout the Commonwealth. Since the War, the facility has fallen into disrepair and is inoperable.
Upon entering the facility the maintenance office is located on the right in a metal pod, inside the office are a terminal 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.
- Robot model kit parts - On a metal table just outside the factory, in a Railroad stash (indicated by the railsign) via a brown pipe going into the lake, accessible via an underwater breach in the pipe.
- 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 room behind the security doors and the tool case right next to the key.
- Cleansing the Commonwealth - This is one of the locations Knight Rhys will ask to cleanse of its inhabitants.
- Ghoul Problem
- Last Voyage of the U.S.S. Constitution - This is one of at least two destinations to which the Sole Survivor can be sent to retrieve the Poseidon radar transmitter.
- Learning Curve - This is one of the locations where you need to escort a scribe of the Brotherhood.
- Lost Soul - This is one of the possible locations that you may be asked to rescue a synth by the Railroad.
- Quartermastery - Scribe Haylen asks you to retrieve a haptic drive from this location.
- Randolph Safehouse - This is one of the possible locations that may need to be cleared out for Mr. Tims.
- Treasure Hunt
The security doors remain open when the area resets.
The Poseidon Reservoir appears only in Fallout 4.
- PC Playstation 4 Xbox 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.
- ↑ Fallout 4 Vault Dweller's Survival Guide, page 354 - "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."