Use a mid-air horizontal Power Bomb boost to reach the first platform. Jump across to the last platform. Wait until the water is low, let the platform sink slightly, then jump and horizontal Power Bomb boost to the item.

If HiJump is available, then it is possible to simply spin jump from the underwater platform to the first moving platform, saving a Power Bomb. If HiJump cannot be disabled, then the Power Bomb boost from the last platform is more difficult: in this case Samus must jump, lay the Power Bomb on the way down, then jump again to a precise height and morph to get the boost.

Requires:

"f_DefeatedPhantoon"
"canMidAirMorph"
{
  "tech": "canJumpIntoIBJ"
}
{
  "tech": "canBombHorizontally"
}
"canInsaneJump"
{
  "or": [
    {
      "and": [
        "HiJump",
        {
          "ammo": {
            "type": "PowerBomb",
            "count": 1
          }
        }
      ]
    },
    {
      "ammo": {
        "type": "PowerBomb",
        "count": 2
      }
    }
  ]
}
"h_complexToCarryFlashSuit"