I know it is illegal here in Alberta Canada to keep wild birds if they are not banded. The fine is very big. Contact your local wildlife office to see if you can even keep it?
Best of luck!
I have chickens and ducks I have a duck who was raised by a chicken a silkie. She now after a year and a half now intermingles with the ducks but choses to roost like a chicken eat like chicken. Runs to me like the chicken when I have treats. We say she is a dicken. We lost her momma to a brooder fire. But she feels more comfortable with the chickens I recently started keeping my three other ducks in the coop with the chickens I think that's why she now intermingles with the ducks. The only problem I see is if your little duck is a male because chicken and ducks cant mate they are made differently. I did have three male ducks with my chickens and I didn't have a problem except that my one male was in love with the silkie so she stayed in the coop away from him or he would chase her. Good luck with your duckling. Ducks eggs are wonderful. My ducks lay better than my chickens. spend as much time as you can with her. hopefully one of the chickens will adopt her.
duck do like to swim they don't get there own oil in until they are older not sure of your breed but you could look that up so make sure you let her swim but then dry her really good . Don't let her swim on her own because they get tired and could drown. I was amazed when my ducks raised their chicks that the chicks were only hours old and they would swim and swim. When duckling are raised by ducks the chicks rub themselves under the adults so their oils get into their feathers . They don't make their own oils until older. I use a kiddie pool for swimming.