Chickens have been raised on farms with ponds for thousands of years. Farm ponds are traditionally where farm raised free ranging chickens get water. They do not go swimming, but as long as the banks are not so steep that they cannot get out, chickens will not drown if they somehow fall in. Down-covered chicks are different. They will drown if they get in water, but they will not voluntarily jump in. If adult chickens cannot walk out, they will drown since their feathers are not oil covered like ducks and the feathers will eventually get wet and eventually pull them down. They can swim for a while.
I don't know what your area looks like or how it would be set up, but unless you had something strange, I would not expect a chicken to be in any danger of drowning. With certain set-ups, I would expect ducks to make a muddy mess if the drainage around it is not good and they are in a small space, but that was not your question.
Good luck!!!