fluten
to flood
To inundate or cover an area with a large amount of water.
Nach dem Deichbruch wurde das gesamte Polderland geflutet.
After the dike broke, the entire polder land was flooded.

to flood
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to flood
To inundate or cover an area with a large amount of water.
Nach dem Deichbruch wurde das gesamte Polderland geflutet.
After the dike broke, the entire polder land was flooded.

The verb 'fluten' (to flood) is closely related to the noun 'die Flut' (flood, tide). This connection helps you understand the basic meaning of a large, flowing mass, whether it is water, people, or data.
Die Flut kam schneller als erwartet und begann, die Küstenstraße zu fluten.
The flood came faster than expected and began to flood the coastal road.
The perfect tense is usually formed with 'haben' when something is actively being flooded. However, if the movement of many people or things to a place is being emphasized, 'sein' is often used.
Der Sturm hat viele Keller geflutet.
The storm flooded many basements.
You can recognize the figurative meaning by the fact that the subject is not water, but people, information, or objects. The verb then describes something streaming to a place in overwhelmingly large numbers.
Nach der Ankündigung des neuen Produkts fluteten die Bestellungen die Website.
After the announcement of the new product, orders flooded the website.
In the figurative meaning, 'fluten' (to flood) is often combined with subjects like 'Touristen' (tourists), 'Fans' (fans), 'E-Mails' (emails), or 'Nachrichten' (messages), and objects like 'die Stadt' (the city), 'das Stadion' (the stadium), or 'der Posteingang' (the inbox).
Jeden Sommer fluten Touristen die kleine Küstenstadt.
Every summer, tourists flood the small coastal town.
The meaning 'einen Hohlraum füllen' (to fill a cavity) is technical language. It is used in technical or medical contexts, for example when cleaning a system or flushing a wound.
Der Arzt musste die Wunde mit einer antiseptischen Lösung fluten.
The doctor had to flush the wound with an antiseptic solution.
to fill
'füllen' and 'fluten' can both mean that something enters a room, area, or system and makes it full. 'füllen' is neutral and controlled: you fill a glass, a tank, or a room with something. 'fluten' sounds stronger and often refers to a very large amount, especially water. It can also mean that very many people, messages, or things arrive all at once. Learners may confuse the words because both have to do with 'making full'. When something is normal and intentional, people usually say 'füllen'. When something streams in in large quantities or covers everything, 'fluten' fits better.

Nach dem starken Regen flutete das Wasser den Keller.
After the heavy rain, the water flooded the basement.
Sie füllt den Eimer mit warmem Wasser.
She fills the bucket with warm water.