die Flut
high tide
The period during which the sea level rises, in contrast to low tide.
Bei Flut kann man hier nicht am Strand spazieren gehen.
At high tide, you can't go for a walk on the beach here.

tide / flood
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high tide
The period during which the sea level rises, in contrast to low tide.
Bei Flut kann man hier nicht am Strand spazieren gehen.
At high tide, you can't go for a walk on the beach here.

'Flut' (tide / flood) is related to the verb 'fließen' (to flow). It describes a large, flowing movement of water—or, in a figurative sense, of other things.
Nach dem Dammbruch flossen riesige Wassermassen ins Tal.
After the dam burst, huge masses of water flowed into the valley.
If people are talking about the sea, the tidal meaning of 'Flut' is meant, often in the pair 'Ebbe und Flut' (ebb and flow / low tide and high tide). If it is about a water-related disaster, a flood is meant. A 'Flut von' (flood of) something abstract is always the figurative meaning.
Wir müssen warten, bis die Flut zurückgeht, um die Muscheln zu sammeln.
We have to wait until the tide goes out to collect the shells.
'Flut' (high tide) is very frequently used together with its opposite 'Ebbe' (low tide) as the fixed pair 'Ebbe und Flut' (low tide and high tide) to describe the tides.
An der Nordsee bestimmt der Rhythmus von Ebbe und Flut das Leben.
On the North Sea, the rhythm of low tide and high tide determines life.
In the figurative meaning, 'Flut' (flood) is almost always used with the preposition 'von' (of) and a plural noun. This construction describes an overwhelming amount.
Nach seiner Rede erhielt er eine Flut von Glückwünschen.
After his speech, he received a flood of congratulations.
sea
'das Meer' and 'die Flut' both have to do with large amounts of water, but they are not the same thing. 'Das Meer' is the large body of salt water. 'Die Flut' describes a movement or situation: the water rises, or water floods land. On the coast, 'Flut' is the opposite of 'Ebbe'. Both words can also figuratively mean a very large amount. Learners may confuse them because both sound like a lot of water. The important point is: das Meer is a place or a body of water, while die Flut is an event or a high water level.

Bei Flut steht das Wasser bis an die Treppe.
At high tide, the water reaches all the way to the steps.
Nach der langen Fahrt freut sich meine Schwester auf das Meer.
After the long drive, my sister is looking forward to the sea.