During the journey along the subway, Artyom finds a boat, which has to be used when passing through the next areas of the facility. The following section of the Metro Exodus Guide contains a description of this stage of the game.
Go into the boat and swim forward. You will pass filthier and filthier walls and the interior will start to resemble an organic creation. Watch out for the bugs and swim forwards all the time. You will float into a large room and you will be attacked by big tentacles. Enemies emerge from the water and dive from time to time - try to target and shoot enemies as quickly as possible.
The tentacles will try to blast you into the water, so be careful and kill them as soon as possible. Next, enter a corridor full of green lights and go up the stairs. Kill more tentacles and avoid all their attacks - they're very powerful. Get into the infected carriage and continue through it.
Kill more tentacles and walk up the stairs. Continue until you reach the lever - use it to lower the stairs down. Go down with them and enter the corridor. Kill the big red maggot and go further down the narrow passage.
Go through the slippery rooms until you reach the generator - use it to lower the next boat. Go downstairs and kill the next tentacles that emerge from the water. After it's done, enter the boat and proceed forward.
At the end of the room, another more water beasts will appear. Pull out the weapons and shoot them, then continue rowing and run away from this slimy spot.