List of rooms in Metroid Fusion/Sector 4 (AQA)

This is a list of all rooms in Sector 4 (AQA). There is 48 rooms total. 
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All the rooms in Metroid Fusion have explicit identification numbers visible through access with the Debug Menu. Within the Debug Menu, the values "H" and "G" are used to represent Samus's location on the BSL Station. The "H" Value represents which room Samus is located in, and the "G" value is used to represent the entrance Samus used in order to access the room. For the purposes of this list, the "H" value of the room will be listed first, followed by the "G" value of the first entry into a room, then the "G" values of other entrances in order of normal availability to the player. For example, the Operations Deck would be listed as "H014-G141 (G065, G027, G022, G193)".
If a proper name for the room exists, that name will be put first, followed by the room's "GH" value. Then a short description of the room will be given, possibly with a picture, as to allow for identification of the room. If the "G" value has a Security Lock over the Hatch, the "G" value will be labelled by a color corresponding to the Security Level if the door has a security level greater than 0. If a latent ability is required to use the entrance, an abbreviation for the upgrade will be placed next to the "G" value of the room, such as PB for Power Bomb or MB for Morph Ball. A majority of the room names are unofficial.
==Elevator 4 to Main Deck==
Room ID: h028-g000 (g057)
The Transport to the Main Deck from Sector 4 (AQA). Interestingly, this is the only Sector elevator that leads Samus leftward into the sector (all other numbered elevators lead rightward into its respective sector).
;Items
:• None
;Connecting rooms
:• Elevator 4 (elevator)
:• Sector Navigation Room (gray hatch)
==Navigation Room Station 4==
Room ID: h003-g001 (g007)
The Navigation Room connecting in-between Sector 4 and the elevator to the Main Deck. 
Of major importance, it is within this room where Samus is informed of the creature known as Serris. She is given a mission to terminate the specimen to prevent it from causing anymore damage onboard the B.S.L.. She returns to this room after the task is complete and the water is drained from the Pump Control Unit. During the next uplink, Samus is instructed to uplink at Sector 3's Navigation Room for further instruction. 
Samus returns to this room after obtaining the Diffusion Missile upgrade. Here she is scolded by the Computerized CO. for opening the Level 4 Hatches without permission and is then redirected to Sector 6. The Secret Message also takes place within this Navigation Room.
==Save Room Station 4==
Room ID: h002-g005 (g006)
The main Save room of Sector 4 (AQA). Like the other main Save rooms seen in other sectors, it connects to both a Recharge room and a Navigation Room. The only difference being the Nav room is located towards the Eastern hatch and the Recharge room is positioned on the left-hand side.
==Recharge Room Station 4==
Room ID: h030-
*g061: (Right Door) 
*g099: (Left Door)
The main Recharge Station of Sector 4 (AQA). Unlike the other Sectors, the entrance to the Main rooms of this sector are located towards the leftmost direction, whereas the Save Room is towards the right.
==Sector 4 Main Hall==
Room ID: h001-g002 (g003, g058) 
This room is the Main Hall of Sector 4, connecting the Western areas and access to Underwater deep areas. This is the only Sector Main Hall completely devoid of any enemies whatsoever.
==Sector 4 Access==
Room ID: h006-g011 (g012)
This hall leads to the entrance of the entire overwater sections of Sector 4. The room's only inhabitants are two uninfected Scisers in the background (one normal and one gold). When Samus returns to this room after draining the water, the doors lock and she is forced to defeat an X infected Sciser, then an X infected Gold Sciser to escape.
==Main Research Pool==
Room ID: h007-g013 (g014, g018: SB, g065: Roof), 
A rather large room with many blocks hanging from pairs of chains from the ceiling. This is the first room Samus visits that contains the main overall backdrop of Sector 4. Upon entering for the first time, Samus must clear a large bombable brick leading to some Monkey Bars on the ceiling, then carefully climb and/or stand on the hanging blocks to avoid falling into the electrified waters below. Many Scisers hang from not only the walls and roof but also on top of the chained blocks themselves, so Samus may need to clear some Scisers first before progressing to the top-left door.
After Serris has been defeated, Samus once again enters this room. This time from a wide hole in the roof (it is also possible to enter this hole during the first visit, allowing access into the next room). At this point, Samus cannot return to the Navigation Room due to her only exit being too high to climb. Samus must backtrack out of this room until she discovers and activates the Pump Control Unit. With the water drained, Samus can then re-enter this room and perform a Speed Boost on the floor (after clearing out some Scisers on the ground floor) to destroy a large block of Speed Booster blocks from either the left or right side of this room (with the right stack of Speed Booster blocks leading Samus back to the Navigation Room). Most likely however, Samus will enter this room from the AQA Reservoir whilst Speed Boosting, easily accessing the rightmost door while also running over any floor Scisers.
This room contains 5 Scisers and 2 uninfected Scisers located on the ceiling. The Sciser above the rightmost Door possess an invincible X Parasite. After the water has been drained, the room will possess 3 Scisers and 1 uninfected one. Two Scisers will be on the floor, the one on the rightmost roof containing the invincible X Parasite remains. Because the remaining uninfected Sciser does not move horizontally, sometimes an X Parasite stemming from the floor may circle around the uninfected creature in an infinite cycle as it tries to possess the Sciser.
A Power Bomb Expansion can be located on the lowest center point of this room. First Samus must bomb a reforming Bomb block directly underneath the rightmost pile of Blue (Speed Booster) blocks near the rightmost Door, then follow the revealed tunnel to bomb another block leading her into a large pit area where electrical wires are exposed near two platforms. A hidden Power Bomb block is hidden underneath the set of electrical wires to the left of this pit. Using a Power Bomb will not only destroy this block but also reveal five shot blocks and the hidden Power Bomb. Samus can simply roll in Morph Bomb to acquire the expansion. Any shot blocks that reform can be cleared with more bombs. Samus escapes this pit through the same way she entered.
==Main Aquarium==
Room ID: h008-g015 (g016, g019)
This room has two large tanks built for research purposes. The bottom right one leads nowhere and can prove to be a deadly place to be in should Samus fall in. Near the bottom left hatch, a punctured water storage tank can be seen in the background, its held contents leaking out onto the floor. The top left hatch located inside an Aquarium tank leads to a Save Station, a hall containing a connecting Aquarium, and a room close to Serris's Breeding Tank. 
This room contains many creatures. Initially it holds:
*4 Scisers and one uninfected Sciser, but an additional Sciser can be spawned in by any free roaming X Parasites (it is spawned in the bottom right pool). 
*4 small Skullteras; three in the bottom right pool and one on the top left tank. Two additional Skulltera can be spawned by any free-roaming X Parasites (one in each tank). 
==Aquarium Hall==
Room ID: h009-
*g020: (bottom-right Aquarium Tank Door)
*g021: (Top-left Door to Breeding Tank shaft)
*g074: (Save Room Door)
A long hall containing two punctured Water Tanks, its contents leaking out onto the floor, creating small ponds of water to slow down Samus (before she has obtained the Gravity Suit). Samus can enter this room from the Main Aquarium, which will lead to another Aquarium tank on the bottom of this room. Climbing out of the tank, Samus navigates this long hall and eventually winds up in the next room above, which houses an Energy Tank. Samus ultimately backtracks out of this room towards the Main Aquarium due to damage caused by the X (possibly Serris) in the shaft room connecting to the Breeding Tank. A door directly above the aquarium tank and ladder leads to a Save Station. 
This room contains 4 Scisers. One free roaming invincible X Parasite will appear in the Aquarium Tank as soon as Samus enters from the bottom-right door and this X Parasite will become a Skultera. Should Samus move closer to the left, another invincible X Parasite will appear and immediately attach itself to the Skultera (if still alive and unfrozen), forming the larger variant of Skultera. Should Samus enter this room from anywhere else besides the bottom-right door, both Free roaming invincible X Parasites will appear simultaneously.
==Aquarium Save Station==
Room ID: h033-g062
A marked Save Station located near the Aquarium areas. It is located directly underneath the breeding tank according to the map.
==Testing Tank Access==
Room ID: h011-g063 (g064, g022: E-Tank entrance)
This room leads to the large underwater Tank where Serris is fought. A large metal bar has been smashed in a way that it prevents access to a door leading to an E-Tank. The E-Tank must be obtained from its blocked off connecting room. For Samus to reach through the rest of the room, she must enter from the Breeding Tank, then climb (or wall jump off) a series of ladders leading to a drop into a flooded shaft where the door to the next room awaits. This rooms's only inhabitant is a Gedora X blocking access to Serris's room and is the only Gadora dealt with while underwater.
==AQA Reservoir==
Room ID: h021-g017 (g043, g059SB, g071: hole in roof) 
A wide room filled with electrified water. Samus must locate a way to cross over the electrified pool to the other side of the room. A hidden roof can be bombed to reveal monkey bars leading to a bombable wall. A hole in the top-center of the room leads to a hidden room not initially marked on the map. 
This room contains 3 Scisers, crawling above the water in various surfaces. Once the Pump Control Unit has been activated, the three Scisers relocate to the bottom of the drained pool. 
==Mini-Aquarium==
Room ID: h031-g066:MB (g067: to Breeding Tank, g068) 
Samus can reach this small research tank by climbing up from a hole in the roof by the bombable wall of the previous room. This tank room has a few small tunnels where Morph Ball is required to proceed, however at the end of the maze is a single Crumble Block that will leave Samus right back towards the bottom entrance. If Samus climbs the leftmost ladder all the way to the top, she can enter a hidden Morph Ball tunnel leading into a secret hidden room.
Samus can access the top shaft from a hidden Morph Ball tunnel in the Northwest Save Room nearby. The top shaft connects to both the Save Room (left) and the Breeding Tank (right door).
There are no enemies whatsoever, however the prototype builds reveal that an X Rally point is stationed within this room, suggesting that at one point enemies were intended to be included.
==Secret Pool==
Room ID: h047-g114 MB
A small one-way Aquarium accessed from a hidden Morph Ball tunnel from the Mini-Aquarium. 6 Owtch surround a central platform while a Missile Expansion is stationed in the bottom-left corner of the room.
==Pumping Station==
Room ID: h022-g044 (g046, g075, g045)
A tall room containing many doors and a maze like obstacle course climb to the top. Samus climbs this shaft on her way to encounter Serris. In this room, Samus must grip carefully over some pits and destroy a few blocks to proceed. The Blue Hatch in this room leads to the Pump Control Unit, this room is revisited as Samus passes through here using her Speed Booster. A Red Hatch exists far underneath the water. This Hatch may be passed through should Samus decide to Shinespark her way out of Sector 4 after obtaining the Gravity Suit (this route would normally lead to the Secret Message). 
This room contains 5 Owtch and one Sciser positioned high above the (electrified) water area. Though normally unseen, the camera for this room won't correctly scroll until the large 4x4 block near the right door across from the Blue Hatch is destroyed. 
==Save Station Northwest==
Room ID: h023-g047 (g069:MB)
This Save Station is located in the Northwestern part of upper AQA. Samus comes to this room after an extensive wide search for Serris. Like one of the Save Rooms seen in Sector 1 (SRX), there is a small crack in the rightmost wall. Samus can blast the crack, leaving behind a small Morph Ball sized opening for her to roll into. This hole ultimately leads to the Breeding Tank.
==Breeding Tank==
Room ID: h032-g070 (g073)
As mentioned by the Computerized Co., the Breeding Tank is where Serris was originally held at. During Serris's rampage of Sector 4, it was believed to return here out of natural behavior. When Samus arrives however, there is nothing but the bones of Serris that remain, leading to the to the conclusion that Serris was absorbed by the X parasites. Samus continues through this room into the next to track down the mimicked creature.
The room is void of all life whenever Samus enters. The first time Samus enters this room, Environmental_Sound_(Disquieting) begins to play until Samus reaches the boss room.
==Testing Tank==
Main Article: Serris arena
Room ID: h043-g104 (g026)
This is the room where Serris is fought. Upon the creature's appearance, parts of the bridge above water level will crumble, leaving only smaller platforms to stand on. Once the creature is defeated, Samus obtains the Speed Booster and exits through the top-right doorway (Samus is currently unable to climb out of the water filled shaft from the previously entered room).
==Booster Hall==
Room ID: h010-g023 (g024: SB one way exit)
Samus arrives in this long split hallway exiting Serris's arena. Here she must use her newly reacquired Speed Booster to escape this room. The top half of the hall demonstrates the use of the Speed Booster. At the right side of the hall, Samus must destroy the wall near a suspicious looking floor to gain access to the lower half of the hall. After clearing the Owtch roaming around, Samus can use her Speed Booster uninterrupted to break open a panel on the floor, revealing an exit shaft.
This room contains three Owtch but immediately upon entering, seven invincible X Parasites arrive and three of them morph into three additional Owtch (leaving the remaining four to free-roam around the room for Samus to absorb. The X Parasites lose their immunity once the three additional Owtch are present).
==Water Tank Storage==
 
Room ID: h014-g030 (g029: one way exit, g117: Door to Save Room)
This long hall isn't initially listed on the Map. Samus can optionally choose to come here before engaging with Serris by entering the open-roofed area of the Main Research Pool. Two Missile Expansions are located within a small block maze. To reach them, first Samus must reach the top-right of the room and bomb the row of bombable blocks. Then after following along the morph Ball tunnel will she need to bomb another row of bombable blocks. The first Missile Expansion is located hidden in a small Morph Ball crevasse to the left of the ladder. Using the nearby ladder, Samus must then destroy two Missile Blocks to enter a hidden tunnel. It will lead to a left-most area where she must carefully jump rightwards to a dead-end area leading to the left of the second Missile Expansion (should she fall, a small pit of one-way Crumble Blocks will be waiting for her below). The wall near the second Missile Expansion is breakable, and three large shootable blocks are all that is left in the way of this Missile Expansion. 
After defeating Serris, Samus enters this room from above after escaping the Booster Hall. At this time, she can then choose to obtain the two Missile Expansions nearby if not yet obtained.
This room possess three roaming Owtch along with the two aforementioned Missile Expansions.
==AQA Storage Save Station== 
Room ID: h012-g025
A Save Station is located within the unmapped area of Upper AQA, in the Northeastern area. The door to the left leads to the Water Tank Storage.
==Pump Control Unit==
Main article: Pump_Control_Unit
Room ID: h034-g076
The Pump Control Unit, a large room where water flow controls are maintained. This room is guarded by a Level 1 Security Hatch, but will be open by the time Samus can reach this room due to her previous actions in Sector 2. This room features a long hallway which is suitable for Speed Boosting. The controls are inactive until Serris is destroyed, and even then Samus would need the Speed Booster to enter the control area, due to its gate being composed of Speed Booster blocks. Once Samus activates the terminal, all the water within Sector 4 that isn't housed in aquarium tanks will be drastically lowered, allowing for Samus to explore further the depths of Sector 4 and being safe from electrified water (though electrified wires are still a hazard). 
This room contains no enemies but does contain one Missile Expansion directly below the computer terminal.
==Secret Aquarium==
Room ID: h029-g060 (g004)
This small and wide research tank is hidden from normal map's view, located underneath the larger tanks' room. It is discovered once Samus Speed Boosts into this room from one of its connecting rooms after the water has been drained from the Pump Control Unit. While there is no life available, a Missile Expansion is housed inside the wide research tank, positioned from the leftmost side. Samus would need to enter the research tank by climbing in from the rightmost side, as the left edge is blocked by a crumble block exit. To save time, it is possible to build up a Shinespark before Samus enters the tank, then quickly release a Shinespark to the left once inside the tank. The water will not slow down Samus if she is Shinesparking.
There are no hatches towards either exit, only Speed Booster Blocks positioned in both adjacent rooms. Samus must build up speed using the Speed Booster to escape this room. 
Interestingly, this room is never shown to be flooded, even when the Speed booster blocks are destroyed before draining the water via debug menu (though the blocks regenerate as Samus enters another room).
==Maintenance Bay==
Powamp-X Screen1.jpg|Samus in the Maintenance Bay.
Maintenance Bay (Full).png|Full view of the room.
Sector 4 Diffusion Room JP.png|The Japanese version of the entire room.
Room ID: h004-g008 (g009, g027, g084) 
Main article: AQA Maintenance Bay
A large room positioned directly underneath the main Recharge and Save Rooms. This room reuses the backdrop from the tall shaft of the Docking Bays, suggesting heavy operations were done within this room for Sector 4. Samus enters this room on her way to reach the Data Room containing the Diffusion Missile upgrade. It is possible for Samus to visit this room as early as accessing the main hall of Sector 4 however. 
This room contains 3 Powamps (two Powamps in the Japanese version)
==AQA Maintenance Tunnel==
Room ID: h037-g085 (g091, g092)
This tunnel runs underneath the Main Hall and can be accessed from the Maintenance Bay. The room has electrical currents exposed outward from the walls so the water will be electrocuted when Samus enters. A Powamp hides underneath a Morph Ball tunnel, preventing further access or exploration by Samus. A Geron blocks access to the leftmost corner of the room, where a Missile Expansion is available, hidden inside the walls underneath the exposed electrical wires. A shutter above the Geron also blocks access to the hidden Missile Expansion.
Once the Pump Control Unit has been activated, the water in this room will no longer be in contact with the exposed electrical wires, allowing for safe travelling. To reach the Missile Expansion, Samus must either destroy the Geron blocking access to it or activate the shutter using the Wave Beam. Alternatively, Samus can run quick enough past the Geron's spawning position before it is formed the moment she enters the room.
After the water has been drained, the Powamp is removed, allowing Samus to explore further. Underneath the Morph Ball tunnel is a small hall containing two doors further leading into the depths of Sector 4. The right door leads to a room containing another Missile Expansion, but beyond that, Samus cannot explore this Sector any further due to the interference of the X infected creatures. 
After the Gravity Suit has been obtained, the missing Powamp returns, blocking Samus from easily escaping Sector 4. Forced to find another way out, Samus can use the lower part of this room to build up Speed or a Shinespark for use in the lower adjacent rooms. Once the Diffusion Missiles have been obtained, they can be used on the Powamp in this room to once again be able to travel between the Morph Ball tunnel. 
This room contains one Missile Expansion, two free-roaming X-parasites, and a Powamp. Upon entering the room, one free-roaming X Parasite will immediately turn into a Purple Geron unless the Geron was destroyed. The Powamp disappears once the water is drained from the Pump Control Unit but will reappear once the Gravity Suit is obtained and cannot be destroyed due to its positioning.
==Algae Hall==
Room ID: h039-g093 (g094)
This long room connects the upper portions of Sector 4 to the lower. Samus can explore this room as early as after drainign the water from the Pump Control Unit. A Missile Expansion in this room is available to acquire during this time. There is a Kago present in this room that immediately grows upon Samus's presence nearby. It will block access to a hidden tunnel leading to a Power Bomb Expansion and the rest of Sector 4 depths, but if Samus has the Gravity Suit, the Kago will remain pillar-sized upon entering and the pillar will relocate closer to the door, blocking access to the Missile Expansion if not yet obtained. At this time, should Samus have missed the opportunity to acquire the Missile Expansion early, she would need to either locate the hidden tunnel from this room's right side or would need to destroy the Kago to proceed through. 
To acquire the Power Bomb Expansion, Samus would need to build up speed in a long room below, then Shinespark into a hole in that room's roof. If done correctly, Samus will Shinespark into this room from below, breaking the Speed Booster blocks blocking access to the Power Bomb expansion.
This long room contains three Yards, a Kago, a Missile Expansion and a Power Bomb Expansion. Before obtaining the Gravity Suit, an invincible X Parasite will immediately enter the room and attach itself to the Kago once Samus nears the Missile Expansion from the left side of the room. After obtaining the Gravity Suit, the Kago remains fully grown at all times and is relocated closer to the left side of the room, the invincible X Parasite no longer appearing.
==Main Seabed==
Room ID: h020-g042 (g055: to Algae Runway, g090: top right door, g116: to Save Room)
A large room where most of the undersea life dwells in Sector 4 (AQA). This room serves as the main entrance towards the deeper portions of Sector 4, or the exit out of the deep.
Samus can optionally choose to explore this area as early as after draining the water from the Pump Control Unit. Samus won't get far however, as a Powamp prevents access through a small tunnel, blocking it with its entire body once Samus draws near. Later after Samus obtains the Gravity Suit and exits out of Sector 5 (ARC), she reaches this room after unlocking Level 4 Security hatches, still seeking a way out of Sector 4. After navigating a small maze, Samus can reach and freeze the aforementioned Powamp from its left side, allowing Samus to escape this area. She will be stuck still however, unless she can use this room to build a Shinespark for use in the connecting two rooms in the top-right area. Alternatively, she can use those two mentioned rooms to activate her Speed Booster to break two hidden Speed Booster blocks on the floor located between the Powamp and the top-right door. This will allow Samus to bypass a previously encountered Mutated Kago blocking part of the room. The right side of the mutated Kago has a door leading into the Algae Runway, another room for building up speed for the Speed Booster. The bottom left door leads further into the deep portions of Sector 4, while the bottom right door leads into a Save Room.
This room contains 5 Yards, a Mutated Kago, and 2 Powamps.
==Hydro Transit Station==
Room ID: h024-g048 (g053, g077: Left tube to Sector 5, g078: MB
An underwater Station linking Sector 4 (AQA) to many other facilities. Towards the bottom left is an underwater tunnel leading to Sector 5 (ARC). The top right Red Hatch leads to the Pump control Unit, and the top right section leads to the underwater sections of Sector 4 (AQA). 
Samus runs through this room during her escape out of Sector 5, after she has obtained the Gravity Suit. She must use her Speed Booster to break a wall of Speed Booster Blocks blocking access to the top right door leading to the deepest portions of Sector 4.
This room contains 7 Skulteras and 3 Scisers. An 8th Skultera may be spawned near the Red Hatch by any free-roaming X Parasites in the room. A Power Bomb Expansion is located below the wall of Speed Booster blocks, completely sealed off from this room. Samus would need to locate hidden Morph Ball tunnel in an adjacent room to obtain said Expansion.
==Hydro Shaft==
Room ID: h015-g031 (g032, g033: bottom-left door, g034: bottom-right door, g079MB, g096: top-right door to the Save Room)
A tall access shaft in the deep zones of Sector 4. This room has five different access points. Once Samus enters this room from the Hydro Transit Station, Sector 4 Underwater theme begins to play.
This room contains
==Hydro Save Station==
Room ID: h040-g097
A Save Room located in the underwater depths of Sector 4 (AQA). Can first be accessed by Samus during the underwater visit into Sector 4 (AQA) after obtaining the Gravity Suit.
==Hydro Hall==
Room ID: h016-g035
This long one-way hall contains many enemies, a few places where shot blocks are lined up together, and a Missile Expansion at the back of the room. This leads to a dead end so Samus must turn back to where she entered from.
This room contains 7 Yards and 1 Red Zeela. A missile Expansion is located at the right edge of the room, in plain sight.
==AQA Security Hall==
Room ID: h025-g054 (g049)
A tube-like area inside a large cave.
This room initially contains 4 Skultera and one Evir. Any free-roaming X-Parasites near the tube will turn into an additional Skultera, followed by that same X Parasite becoming invincible and turning into yet another Skultera. If two X parasites are left to free-roam simultaneously, near the room above the tube hall, an additional Evir will form. OTherwise any singular X parasite will fail to form into an Evir and simply float away (if possible). Most X Parasites in this room either float rather quickly or are invincible.
A Power Bomb Expansion is also present within this room. It is located in a small cave located on the top-right corner of this room. After entering the area on top of the tube hall, Samus must destroy Bomb blocks positioned on the right algae-filled wall, close to the ceiling. A Power Bomb can easily uncover the hidden Morph Ball tunnel leading to the Power Bomb Expansion. 
Oddly, the Red Hatch isn't listed on the map. The same is true for its opposite side. It is possible that a change was made during development and the developers may have forgotten to update the map. This change in the door may have been made to force Samus into seeking the alternate route above this room, or this room may have had a different layout in very early builds.
==AQA Security Access Shaft==
Room ID: h026-g050 (g051, g083, g100:MB) 
The shaft connecting the deep southwest portions of Sector 4 to the Level 4 Security Room. A hidden Morph Ball tunnel is located east of the nearby Sciser, next to a small ledge in the wall.
This room contains 6 Scisers stuck inside a wall. Given their position, they are harmless to Samus and out of reach from her. A Power Bomb can dispatch these foes and draw out their X Parasites however. 
Oddly, the Red Hatch on the top-right corner of the room leading to the tube hallway is not marked on the Map. The same is true for its connecting opposite side within the adjacent room. It is possible that a change was made during development and the developers may have forgotten to update the map. This change in the door may have been made to force Samus into seeking the alternate route in the nearby tube room, or this room may have had a different layout in very early builds.
==AQA Security Roof==
Security Roof (Full).png|Full room view.
BSL AQA Screen1.jpg|Samus in the tunnel maze.
Room ID: h035-
*072: Morph Ball tunnel (one-way entrance to Security Room)
*081: Top-right entryway
*082: Center-right entryway
An algae and coral area located in the furthest westmost points of Sector 4 (AQA). There are many blocks that can be bombed, and this room is positioned directly above the Level 4 Security Room. The right hallways leads to previous algae and coral rooms. 
Samus traverses through the watery maze in order to locate an exit out of Sector 4 (AQA). On the lowest elevation, a Morph Ball maze exists to confuse Samus, but with careful navigation, she eventually locates a small underwater vent leading directly into the Level 4 Security Room. 
This room initially contains 4 Skultera and 1 Evir; two Skultera each on both the center and lower areas while the Evir is on the top caveway. Immediately upon entering this room, three invincible X Parasites enter; one attaching itself to a center-left positioned Skultera and the other two forming an additional Evir on the top caveway.
==Security Room Level 4==
Room ID: h027-g052, g098: one-way roof)
The Security room for all Level 4 Hatches. Samus enters from the roof through a secret air vent, then accesses the terminal in order to unlock all Red Hatches, allowing to continue seeking an exit out of Sector 4.
If Samus lays a Power Bomb immediately before stepping on the terminal platform, the Red Hatch towards the right will be opened while Samus is still accessing the terminal.
==Sciser Cave==
Room ID: h041-101 MB (g102: Locked Door)
A small algae and air-vent filled crater dug deep underneath Sector 4 (AQA). It is accessed via a hidden Morph Ball tunnel, located to the right of the Level 4 Security Room shaft. Six Scisers are out of reach within a small enclosed corner to the bottom-left of this room. Samus must destroy them but also not absorb some of the free roaming X Parasites, until one or two of them latch onto the uninfected Gold Scisers in the right side of this room. The Golden Scisers are immune to Power Bombs so Samus must destroy two hidden Missile Blocks to reach the Gold Scisers at close range, then being able to fire her Charge Beam or Missiles at them. Alternatively, Samus can wait until she has obtained the Wave Beam to fire her charge shots at the Scisers through the walls. to reach the sealed/unlocked door, Samus must destroy a few fake blocks blocking near the doorway. 
This room contains 6 Scisers and 2 uninfected Gold Scisers (which can become X Infected Gold Scisers by any free-roaming X Parasites). The X-infected Gold Scisers must be destroyed in order to enter the storage room to the right.
==Deep Crevasse==
Room ID: h042-g103
This room contains 3 Owtch and a hidden Energy Tank in a small Morph Ball maze. A Power Bomb can uncover the Energy Tank and clear out the Owtch. Samus must climb to the highest point of this room to get the Energy Tank hidden within the Morph Ball maze.
==Hydro Tube East==
Room ID: h018-g039 (g038)
An underwater tubelike structure area connecting more sections of deep Sector 4.
A Missile Expansion is hidden at the bottom of this room.
==Deep Trench==
Room ID: h017-g036 (g037)
An irregularly shaped tall shaft with a Security Level 4 door at the top-right of the room leading towards the outside eastern areas of Sector 4 (AQA). This room has nothing of importance except the usual enemies roaming around.
This room contains two Evirs and two Skulera. A third Skultera may present itself if any X Parasites are left to freeroam around the room.
==Deep Trench Access==
Room ID: h019-g040 (g041)
A small tube leading out of Sector 4's depths. The Red Hatch leads further into the great depths of Sector 4 (AQA).
This room contains two Scisers. One is above the tunnel and one is below, out of Samus's reach and out of harms way. A Power Bomb (or the Wave Beam, if returned here with it) can destroy these two harmless Scisers, exposing their X Parasites.
==Algae Runway==
Room ID: h013-g087 (g088, g095: roof)
A long hall leading in and out of the deep portions of AQA. This room contains 6 Yards: 4 nesting on the roof of the long hall and two on the floor. Once some of the Yards have been cleared out, Samus can use this long hall to build up a Shinespark and unleash it upwards on an open roof leading to the next room's Power Bomb tank.
==AQA Maintenance Shaft==
Room ID: h036-056 (g028), g109, g112:MB)
This tall shaft connects the upper portions of the Sector with the lower portions. Samus would need to climb to the top of this shaft on her way out of Sector 4. A few enemies float about and can be frozen by Ice Missiles, but can also easily be avoided using Space Jumps. Two missile blocks block access into the upper left room. 
Two more missile blocks block access to a hidden hall leading to a tunnel connecting into Sector 6 (NOC). Although it would appear that Diffusion Missiles are needed to access this hidden room, it is possible to enter early using a Diagonal missile shot on one of the Missile bocks. 
A hidden shaft can be accessed below the waters of this room if Samus has the Screw Attack in her possession. She can break the Screw Attack blocks on the floor, revealing an underwater door leading into a tunnel connecting to Sector 2 (TRO).
Interestingly, with the way the ladders are positioned in this room combined with the enemy placement, it is possible that at one point in development this room was to be navigated before obtaining the Space Jump. 
==AQA Maintenance Access==
Room ID: h038-g087 (g086)
A small room containing seven enclosed Owtch. To cross into a next room, two rows of bombable walls must be bombed, however this may cause the four high-positioned Owtch to drop from above if positioned directly above Samus. Alternatively, Samus can simply clear this room with a single Power Bomb. The Level 4 Hatch leads closer to the Data Room.
==Data Room (AQA)==
Room ID: h005-g010
The Data Room located in Sector 4 (AQA). It is sealed by a Level 4 Hatch. It is here where Samus obtains the Diffusion Missile upgrade and is the final Data Room Samus uses.
The computerized CO. first mentions this room after Samus has defeated Serris and has drained much of the water throughout Sector 4 via the Pump Control Unit. When next she uplinks at a Navigation room, Samus is informed that the Galactic Federation has sent her more support Data at this Data Room, this time being Missile Data. Although stated that she desperately needed this, the computerized CO. tells Samus that the room is sealed by a Level 4 Security Hatch, the highest level of security, and suggests to avoid opening sensitive areas unless it was necessary. Samus is then redirected to use the Data Room in Sector 3 and the AQA Data Room is avoided for a majority of the mission.
After Samus defeats the Nightmare in Sector 5 (ARC), she is forced to take a detour out of the Sector. She finds herself returning to Sector 4 and is forced to unlock all Level 4 Security hatches. Still seeking a way out, Samus eventually ends up in this Data Room and downloading the Diffusion Missile data sent earlier by the Galactic Federation. She uses this newfound upgrade to finally return to Sector 4's Navigation Room. This Data Room room is never used again nor does it hold any further significance afterwards. 
Should Samus skip this room after opening the Level 4 hatches and proceeding to a Navigational Room afterwards, she will be greeted by a Secret Message, then forced to "return to the correct route immediately" (Samus cannot fully leave Sector 4 until after obtaining the Diffusion Missiles in this room). 
It is later revealed by the Computerized CO. that the Galactic Federation originally meant to withhold the Diffusion Missile data in an effort to avoid Samus from becoming too powerful, but it was sent too late. It is unknown if the data was originally planned to be sent to this Data Room specifically or it ended up here by chance. 
==Save 4 Southeast==
Room ID: h048-g115
This Save room is located in the eastern part of the underwater environmental area of Sector 4. 
==Transport Tube Access==
Room ID: h046-g110 (g111: MB)
A small uninhabited connecting room. Plays Sector 4 Underwater theme upon entering the room. During her escape out of Sector 4, Samus can destroy the hidden Missile Blocks in the previous room, then enter a hidden Morph Ball Tunnel leading into this room. The left side of this room leads towards the shaft connecting the upper and lower portions of Sector 4 while the door on the right leads towards the transport tube connecting to Sector 6 (NOC).
==Sector 4 Tunnel to Sector 2==
Room ID: h045-g107 (g108)
This tunnel leads into Sector 2. Initially, Samus would only be able to enter this tunnel if she has the Screw Attack in her possession, due to both sides of the tunnel requiring the destruction of Screw Attack blocks to proceed. 
==Sector 4 Tunnel to Sector 6==
Room ID: h044-g105 (g106)
This tunnel leads from Sector 4 into Sector 6 (NOC). Samus can enter this tunnel before obtaining the Diffusion Missile upgrade, but she will be unable to proceed any further into Sector 6 without the Screw Attack in her possession due to Screw Attack blocks blocking access in Sector 6.