The Mexican government has created a large marine reserve around a group of islands home to hundreds of species including rays, whales and sea turtles.
The Revillagigedo Archipelago is a group of volcanic islands off the country's south-west coast.
With a protection zone of 57,000 square miles (150,000km), it has become the largest ocean reserve in North America.
The move will mean all fishing activity will be banned, and the area will be patrolled by the navy.
It is hoped the move will help populations hit by commercial fishing operations in the area recover.
The park was designated by a decree signed by Mexican President Enrique Pena Nieto. It will also forbid natural resources being extracted from the land or the building of new hotel infrastructure.
The area, which is about 250 miles (400km) south-west of the country's Baja California peninsula has been described as the Galapagos of North America, because of its volcanic nature and unique ecology.
Sitting on the convergence of two ocean currents, the islands are a hub for open water and migratory species.
It has hundreds of breeds of ocean wildlife, including humpback whales that use the shallow and coastal areas around the islands for breeding.
Last year the Pacific Ocean site was named as a UNESCO world heritage area.
María José Villanueva, the director of conservation of WWF in Mexico, described the move as an "important precedent" to the rest of the world, according to local media.
It follows a similar move by Chile, which created an even bigger ocean reserve in 2015.