You do not need a certification to see the best of this reef. Most of Bira's coral colour and reef-fish density sits in the top five metres, which is snorkelling depth — so a mask and fins get you a genuinely good day, not a consolation prize.
Start with the house reef. From Bara Beach you can swim out over sand and reach live coral within a few minutes, in water that is usually flat and clear in the morning before the afternoon breeze picks up. Turtles graze the shallows here often enough that guests stop announcing them. It costs nothing but the walk down, and it's the easiest way to fill an hour between breakfast and lunch.
For a bigger day, the reef flats around Liukang Loe Island are the standout. The same fringing reef that divers descend along has long shallow shelves on top — hard coral, anemone fields and clouds of fusilier in three to eight metres of water, with the drop-off visible below you as a blue edge. Boats run there in twenty to thirty minutes from Bara Beach, and snorkellers can share a trip with divers: the boat drops the dive group at the wall and the snorkellers stay over the shallows, everyone surfacing at the same time.
Bring reef-safe sunscreen or, better, a rash guard — the sun on the surface is stronger than it feels in the water. A wetsuit isn't necessary at 27–30°C. If you are snorkelling from a boat, your guide will keep you clear of the channel edges, where current runs faster than it looks from the surface.