Because the load zone for the boss room is below and somewhat near the entrance room, it is possible to reach it with an out of bounds recoil flip.
This alternative spends more time setting up all the way into the corner to make the recoil flip more lenient.
It's possible to skip turning the underwater turnkey by getting onto the waterwheel as Goron and rolling to the other side.
Target the wall in the corner, tap sidehop, and angle Link with an ESS turn or c-up as shown in the video. Dry roll into the water once the platform is down, then turn left, transform Goron, and roll across the wheel with the visual cue shown in the video.
After clearing the Tatl text, tap up on the control stick and immediately shield drop a chu. Run forwards a little bit to get around the wall, then shoot the skulltula. Put on the Great Fairy Mask as soon as possible, then follow the same setup used without fairies (see above). The second fairy sometimes doesn't directly into Link; if it begins circling instead, go for the roll across the waterwheel, then put the Great Fairy Mask back on on the opposite side to get the fairy to come to Link.
Four distance hovers span the gap.
This grants access to rooms that are only meant to be accessed after changing the first waterwheel's direction.
Link will void out if he's ever swimming in water that doesn't have ground beneath it, so this setup aims to keep him above the tunnel the entire time.
To load the room, transform human, get in the corner between the loaded water and the wall, crouch stab right to push Link into the water, and superswim until the room loads.
Original video by Gigo
Load the waterwheel room and align Link to the left of the dark line on the wall. This is directly underneath the only OoB location in the tunnel, so it won't work on a different wall. Do 3 wall hovers up, making sure to get an angle change. On the next hover, hold up to stop your momentum, and end your hover once under the tunnel. Once there, turn around (use map cursor to help) and do distance hovers back until the background turns blue. At that point, dive with a full bottle or trade item and you will land in the tunnel. The current will take you into the room as it is reversed from what it would normally be.
This requires hovering five times and unlocking the camera before transforming to Zora and grabbing the ledge. Hovering is extremely laggy here, so timing the camera unlock is awkward.
Link will void out if he's ever swimming in water that doesn't have ground beneath it, so this setup aims to keep him above the tunnel the entire time. See the video below for demonstrations with and without collision view on.
This video shows how to hover to the upper door from all three of the nearest platforms.
There are several ways to get the boss key without fighting Gekko. The fastest is a jump as Zora. To set up the jump from the biobaba door, target and shield turn up-right; if setting up without that initial angle, target the wall that the biobaba door is on and shield turn down-left or target the wall behind the two pots and shield turn up-left. From here, hold target until the end of the jump. Get to the area behind the pots, then hold up/up-left to make Link run up-left, as opposed to sidestepping left. Roll shortly before reaching the edge and let go of A so Link jumps instead of diving. If Link gets stuck bouncing instead of grabbing, hold R and mash B until he does a jump attack to land in the window.
The video below demonstrates the jump described above, the ice arrow method, and the Zora long jump method.
Recoil flip towards the alcove when the platform is at the top of its range. This is useful as a backup for the long jump strat above.
To skip using ice arrows to get to the fairy chest as intended, use one of the two options shown in the video below:
Four distance hovers span the gap.