What does it mean when you dream of a stranger that you think you know drowning?

it can mean many things. it can mean that this person is someone that you will meet in the future will become someone you know. and then drown or will be un able to swim.

In dreams, drowning usually represents feeling "over your head" in something or overwhelmed by circumstances. For example, you might be "drowning in homework." In this dream, the stranger represents yourself, and the dream expresses your feeling overwhelmed by something beyond your control.