The "Interior Lake" is an unnamed room in Super Metroid very near the Landing Site in Crateria. As the name states, it is a room mostly filled with water with a column in the middle with a Missile Expansion in top of it. The room normally requires the Grappling Beam, Gravity Suit, or a well timed Shinespark to cross.
One the left of the room is a Blue Door leading to a room very near the Landing Site. Along the ceiling are many Grapple Points, the last few having the Pit Block characteristic to them. Most of the room is submerged in water, with only the edges of the room, and the column in the center being above it. On the top of the column in the center of the room is a Missile Expansion that is too far to jump towards. On the far right side of the room is another Blue Door. Within the water on the left side are steps leading back up to the left door, and there is a Bomb Block at the bottom of the column for use if Samus falls on the right side of it. There are no stairs leading to the right side of the room, so the Bomb Block exists so prevent the game from soft-locking, if Samus falls on the right side of it without the Gravity Suit. The right door leads to the flooded cavern.
There are many ways to go through this room without the use of the Grapple Beam. As Power Bombs are needed to access the room, the room cannot be crossed before they are acquired. There are three methods of crossing the room without the Grapple Beam, each with varying degrees in difficulty, speed, and items required. The simplest method is by using the Speed Booster to Shinespark horizontally across the room, usually through the Missile Expansion. This Shinespark can be charged up in the room to the left, but requires a Spin Jump to be preformed to reach the proper height and avoid the steps leading up to the door.
The second method is by using a Diagonal Bomb Jump across the room, usually using the column in the center as a resting point before the Bomb Jumping is resumed. This only requires the Bomb to preform the trick, and the Power Bomb to enter the room. This method is considerably slower and more difficult than the previously mentioned method, but it can be preformed earlier, allowing Samus to enter the Wrecked Ship, defeat Phantoon, and acquire the Gravity Suit before ever defeating Kraid, or entering Norfair, if used in conjunction with the early Power Bomb Sequence Break in the Red Tower.
The third and final method involves using a Continuous Wall Jump (CWJ) to Wall Jump past the entire room. This is the fastest, but most difficult method to cross this room early, requiring many pixel-perfect jumps, and Wall Jumps to execute correctly. This method can be done at the same time as the one mentioned directly above, but is much faster and more useful for Speedrunning.