Some domesticated geese do fly actually Chinese for one and there is a pic of some Toulouse flying in this goose thread too. Not saying the wings should be clipped because if geese are going to be let loose on a lake that maybe their only means of getting away from a predator. I hope you can keep them inside a fenced in area and safe, They are beautiful geese too. My white Embden gander is a biter, I watch at all times where he is and if he even touches me with his bill I will pick him up and walk around with him always holding onto his neck to keep his bill away from my face. This seems to humiliate him I also have had to pin him to the ground he is hard headed and ornery but I love him and will not let him intimidate me. Today my young Toulouse gander tried to bite me [we're getting close to breeding season in another month] so He got the treatment I picked him up and carried him around for a while too.
Ganders have times when they a less hateful usually between late summer and end of year. a short window, lol They take their job as protector of their mate and goslings very seriously. Another reason they should not be left to wander around a lake where people live that is where they get into trouble.
Bless you for caring about them.