By, in written passives: được / bị … bởi

In written Vietnamese, bởi can name what lies behind an action in a sentence with được or bị, much like English "by": Thành phố bị chia cắt bởi hai con sông lớn. The city is divided by two large rivers. The order is the thing affected, then được (for something welcome or neutral) or bị (for something unwelcome), then the verb, and bởi with the cause at the end.

Bởi is at home with causes that aren't people: a river, a storm, a factor, the market. Khu vực này được bao quanh bởi rừng ngập mặn. This area is surrounded by mangrove forest. You meet it in news and reports, and very often in university papers, where bị ảnh hưởng bởi (is affected by) and được quyết định bởi (is determined by) are stock phrases.

When the doer is a person or an organisation, standard Vietnamese prefers do, placed before the doer and the verb: Dự án do Sở Xây dựng thực hiện. The project is carried out by the Department of Construction. Bởi with people is common in papers and in news translated from English, but editors often change it to do.

In conversation, people rarely use either. They say who did it in an ordinary active sentence: Sở Xây dựng làm dự án này. For a cause, they use vì or do: Đường ngập vì mưa lớn. On its own, bởi, or bởi vì, also means "because"; that's a different use.