Welcome to Mayo Connect! I hope someone here will answer your very good questions about BE and UC, as there is indeed a connection between the two. Attached is a table summarizing the causes of BE.

You mentioned that you swim, which is excellent exercise. I would avoid indoor pools, however, as they can be a source of exposure to NTM. Those of us with bronchiectasis are more susceptible to acquiring NTM lung infections. I'm attaching a paper by a PhD researcher who has done extensive work on ways to reduce environmental exposure to NTM.

Jenn Honda presentation - environmental dangers