Mentioned by Guam 12 days itinerary
World Travel Budget- The Couple Travel Blog
"If trying to snorkel I would go to the Ypao Park Once to the parking lot just head straight out in the water from there. Swim to your left toward the Hilton and you will find coral and fish everywhere. Make sure to check the tide and go close to high tide or it will be extremely shallow and you will not be able to get through some parts of the coral."