A slummy town raised above the flooded city of Chicago

(Placeholder name)

Flimsy shacks suspended on poles atop the roofs of skyscrapers below the water.
There is a smaller, but more sheltered town off the lake, where the people retreat during bad weather and the winter months. But since the lake is their whole livelihood they try to tough it out on the lake as much as possible.

There are no roads. Since the town is built on a lake, they have to use water transportation.

Earthquakes after the nuclear attacks sunk the entire city of Chicago, and the waters of Lake Michigan covered even some of the tallest skyscrapers. 87% of the population perished. The remaining percentage successfully evacuated before the disaster.

Coming back to the city, desperate citizens scavenged what they could find floating on the newly shaped lake, and built raised structures atop the highest buildings, suspended above the lake. This was to be closer to the fauna within the lake, for daily harvesting.

Fish from Lake Michigan

So like, logically, could an entire city be flooded if the sewer system was completely destroyed, sinking a large area of land/buildings so that they were low enough to be covered over by an ocean or lake?
cuz yeah that's the idea I had for this place.

Actually it would probably be an earthquake or something, as opposed to BOMBS IN THE SEWER SYSTEM
lol