“There's been a big oil spill off the coast of Louisiana.”
You are watching the news on TV and they're talking about an oil spill. Your roommate walks by and sees the pictures. He hasn't heard about this news, so he asks what's going on. You answer him by saying this.
There's been a big oil spill off the coast of Louisiana.
You use "There's been a ___" to describe an important event that has happened. For example:
There's been a murder.
There's been an earthquake in San Francisco.
This phrase describes a location in the ocean that's away from the land but close to a certain continent, country, state, province, island, etc.:
off the coast of South America
off the coast of Maui
off the coast of California
You can also include details about which side of a country you mean:
They crashed off the south coast of Cuba