A quick read of the beginning of the book of Zephaniah sounds a lot like Noah and the flood:
“I will sweep away everything from the face of the earth,” declares the Lord.
“I will sweep away both men and animals; I will sweep away the birds of the air and the fish of the sea. The wicked will have only heaps of rubble when I cut off man from the face of the earth,” declares the Lord.
Aside from the minor issue that fish won’t likely be destroyed by a flood, the main problem is that this passage foretells a future event, but Noah and flood happened centuries before.
The flood was God’s judgment over rampant evil in the world. The righteous were saved, the wicked were not.
According to Zephaniah there will be another time of judgment. Jesus talks about this, too. Although God promises he will never again destroy the world with a flood, he doesn’t preclude using other means.
We don’t know when this will occur, but there is no need to worry for those who follow Jesus.