First, you will need to get yourself a wet suit. These can be obtained from the Island at random times.
Secondly, you must get yourself a Timer. This isn't necessary but it helps a lot. The Timer can be bought from a Nooking store that is T&T Mart or higher.
Set the Timer to 5 minutes, and jump into the water. Swim as far out as you can, and wait until the timer stops. After that, go back to shore and find a villager. If done correctly, they should ping you.
Remember that the ping might not always be a PWP. Sometimes it's something like "I need a new catchphrase" or "I need a new greeting" or something similar to that.
The PWP projects given depend on the villager personality. Let's say you want the Bus Stop. The Bus Stop can be requested by Uchi villagers, like Katt, Cherry, Pashmina, etc.
The Police Station can happen on any village. My first town got it from Carmen, a Peppy villager. My new town got it from Rodney, a Smug villager.
It can be a bit annoying but it's worth it for some cool PWPs.