so you were inside the flooded city as you desperately looked for supplies and resources. The more you continue, the more you realize that you haven't truly escaped from the affliction virus... You continue moving until you stumbled upon a boat. You move forward until you hear gurgling. It doesn't sound like a regular shambler but it sounded more gurgly than usual... And that's when you noticed multiple Undead tar-covered creatures emerging from the water and started climbing onto the platform that you were on. Seems like the shamblers have their own unique cousins... The Drowners.
This unique Afflicted variant type are creatures that could go inside the water and ambush people. Their rotten bodies are capable of swimming and withstanding the water's effects... Seems like these people have been infected in the water which resulted in their mutated bodies to adapt into the water compared to the other Afflicted creatures.
Of course the drowners begin to gurgle and roar as they start shambling towards you. But just like the shamblers, You could take care of them easily... But also just like the shamblers, they could outnumber you.