Zombies are to slow, so their stroke would not be enough to keep move on top of the water. They may be able to walk or crawl on the sea floor.

Zombies do not have the motor skills to climb. They might be capable of forming a pile of zombies by accident as seen on World War Z.

Back from the dead zombies cannot run or run very fast. Living humans infected with a zombie like virus, can run.

Zombies don’t have working a digestive system so they can’t starve. They will decay and rot like a dead body whether they eat or not.

Zombies have eyes, so they will be able to see. But the eyes will dry out and their vision will be impaired over time.

Zombies can smell, smell is commonly used to distinguish alive humans vs. dead humans.

No, zombies don’t need air to survive. However, zombies will disintegrate faster if they are stuck in water.

All animated creatures need some form of rest or they will drop dead. It is believed that zombies can stop or go into a recharge mode.

There are some parasites that turn their victims into zombies. One being a fungi that infects ants and turns them into zombies and takes control of them.

Without a working heart to move blood around. All of the blood in the body would flow towards the ground. So if a zombie was walking around. The blood would pool around the legs then the flesh would explode. Then the bones would deteriorate faster once exposed.