Terraria features many elements that change their properties based on the state of the game. These can range from something as major as the game state to minor changes like moon color or sprites. Some changes can be easily identifiable, while others can confuse you.
Water turning red in Terraria indicates the start of the blood moon event. The water will remain red throughout the entire night.
The event triggers randomly and can be a menace to deal with in the extremely early portion of the game. You can also trigger it manually using a Bloody Tear. Therefore, if you encounter this phenomenon, you should be ready for an entire night of zombie onslaught.
What is the Blood Moon Event?
The Blood Moon is one of Terraria’s many in-game events. Some similar events include slime rain and the solar eclipse. This event usually starts occurring in the early portions of the game and stays from 7:30 PM to 4:30 AM. There are several new enemies to fight during the blood moon. However, a blood moon will only occur after consuming at least one life crystal.
The spawn rate of various enemies is buffed, including creatures like Dripplers and Blood Zombies. Moreover, The Groom and The Bride also start to spawn. These creatures drop valuable weapons and accessories that can help you move past most of the early game.
While these spooky mobs do not spawn near houses, they can open the doors and barge if given the chance.
Here are the achievements you can gain from surviving your first Blood Moon:
| Icon | Achievement Name | Prompt |
 | Bloodbath | “Survive a blood moon, a nocturnal event where the rivers run red and monsters swarm aplenty.” |
 | Red Moon Rises | “You have survived the Blood Moon!” |
How to Survive Blood Moon in Terraria
The Blood Moon is a relatively easier event to face. If you are not confident in facing the enemies from this event, you can simply wait for it to pass. You will still claim the achievement since there is no progression bar other than time.
To survive the Blood Moon, you must build an enclosed space without doors. Wait till the night is over, and you are good to go. However, try to kill as many enemies as possible to farm items and resources.
Ultimately, prepare for a zombie invasion whenever you see the water turning red on the surface. You can choose to fight back or ignore the event. You can also encounter red water in underground caves. However, a water body will only turn red during the Blood Moon. You can also gain unique rewards if you attempt fishing during the event.