Can a Catholic baptism be held in a lake?
Can. 857 §1. Apart from a case of necessity, the proper place of baptism is a church or oratory.
Baptism should not take place outside of a church or oratory unless there is some kind of emergency (e.g. in a hospital). However, if it was to take place in an unapproved location it would still be valid. I’m unsure of what would necessitate a Catholic baptism in a lake. If it were to take place it would be illicit but valid.