The untreated human waste may never be dumped in inland waters. This is because it is illegal and may also affect the creature that live in the waters. The untreated human waste must be stored in a reservoir in the ship and later disposed in appropriate sewages that are on land.
Oxygen Depleting can cause Warm water. During summer, The upper layer of the water is lighter therefore it does not mix with the cooler water below. Which soon becomes stagnant. (Oxygen becomes depleted and toxic compounds may produce).
That is one of them. I hope it helps. I'm not so good when it comes to this type of science. But if you ever need help with Anatomy Or anything similar to that. I will gladly help.
Because it allows them to breathe and function.
It might be because making it a hybrid could help get nutrition and other things it needs. I don't know exactly though