Final answer:
The capital and largest city of Dominica is Roseau, which is a port on the Caribbean Sea and has the Roseau River running through it.
Step-by-step explanation:
The capital and largest city of Dominica, which is located on the southwest coast and serves as a port on the Caribbean Sea, is Roseau. The Roseau River flows through this city, enriching its natural beauty and contributing to its infrastructure as a port city. Dominica should not be confused with the Dominican Republic, which shares the island of Hispaniola with Haiti and has a different economic and historical context. While Dominica is smaller and less known for tourism compared to other Caribbean destinations, it is an independent nation with its own unique culture and geography.