Agat Bay is the broad, reef-fringed inlet that defines the southwestern coast of Guam between Apra Harbor and the cliffs south of Umatac. The reef sits a few hundred metres offshore and the shallow lagoon inside is calm, clear, and easy to enter from several points along the village shoreline. Snorkelling is straightforward, with good coral cover on the seaward side of the reef when conditions allow you to cross over.
The bay is much quieter than Tumon Bay on the other side of the island. There are no big resorts, no jet skis, and on a weekday afternoon you may have a stretch of the lagoon to yourself. The water reflects sunset light from the west, which makes the south end of Agat a favourite spot to stop for half an hour on the way back from the south of the island.