They start out full and great but after eating enough food they fill up and explode into their colourful versions, giving you coins (normally Gold Doubloons but later Yen, Rupees, Pounds, Dollars, etc. It's not super stressful to deal with them and you can carry on cleaning and helping the bankimals
The 'threat' is Litterbugs that go away when you hit them with water. (It's a British game I'm pretty sure cause a lot of facts are about the UK.) The loading screen gives you tips and facts about actual pollution stuff.
You pick up bottles, cans and glass bottles and recycle them in their appropriate 'bins' and earn coins. There's this free game on PSN that's basically a slime rancher game but you clean up islands and restore the ecosystem and it's so cute and a nice game.
