If You enter a harbor. see buoy with red and white vertical stripes. What should you do?

This signal is known as the "danger signal" or "warning signal" and is used to indicate that you are entering a narrow channel or fairway and that other vessels should be aware of your presence and take appropriate action to avoid a collision.

The red and white vertical stripes on the buoy also serve as a visual warning to other vessels that they are approaching a potentially hazardous area and should proceed with caution.