The plan was announced at the ADB board of governor's meeting, held last week in Fiji.
The Action Plan for Healthy Oceans and Sustainable Blue Economies targets maritime welfare in the Asia-Pacific.
ADB president Takehiko Nakao said it was part of a more, "resilient future, where humanity and oceans thrive together".
Of the world's 10 rivers carrying the most plastic pollution to the ocean, the ADB said eight were in the region.
Without immediate action, the ADB said about 90 percent of the region's coral reefs could be dead by 2050.
The subsequent collapse of fish stocks would threaten food security and livelihoods, especially in Pacific countries.
The ADB plan includes financing and technical assistance to develop sustainable tourism and fisheries, protect marine ecosystems, reduce pollution, and improve the sustainability of coastal infrastructure like ports.
The plan runs until 2024 and will help the ADB's developing member countries achieve their UN sustainable development goals, including goal 14 - Life Below Water.