Diving Phi Phi Islands

Bida Nai

Koh Bida Nai which means "Inner Father Island" in Thai, is a limestone island that rises dramatically from the sea to the south of Phi Phi Leh. Along with its twin site of Koh Bida Nok, this is regarded as Phi Phi's best dive area.

Above the surface the limestone rock formations are stunning with shades of oranges and whites formed by minerals in the rock. Under the water the walls are covered with zigzag clams, huge gorgonian sea fans and sea whips. There are boulders forming swim-throughs and the areas of staghorn coral are home to thousands of fish.

Descending down the mooring line you'll find yourself on the top of a small boulder formation. Swim into the wall of glassfish below and they will part to reveal a gap in the rocks forming a swim-through. Bearded scorpionfish are often seen sitting on the bottom here so take care with your buoyancy.

On the outer edge of the swim-through on the rock walls you can often see harlequin ghost pipefish and seahorses. Look closely also for boxer shrimps, hinge-beak shrimps and numerous nudibranchs. Moray eels make their home here and enjoy having their heads cleaned by the boxer shrimp.

Moving east around the island you pass small coral bommies and a sloping wall covered with colourful anemones and their resident clownfish. Look out for porcelain crabs on the edges of the anemones.

To the south east of the island is a coral outcrop known as Fantasy Reef. There are lots of common lionfish here, residents among the gorgonian sea fans, barrel sponges and sea whips. Schools of trevally and fivefinger jacks hunt above the reef and are a formidable sight as they make constant raids on the thousands of bait fish. Schools of squid can also be seen. Trumpetfish and filefish hover above the coral along with bannerfish and pufferfish. Look out for the well-camouflaged scorpionfish.

On the way to the reef you'll pass a narrow sand patch and a staghorn coral garden that was quite badly affected by rising sea temperatures a few years back. Leopard sharks are usually seen resting here and blacktip reef sharks are also common sightings patrolling the outer edges. They are quite timid but are usually spotted in the early mornings when diving the Phi Phi Islands.

In the shallower area towards the end of the dive it's possible to see bamboo sharks under the small coral covered rocks. Look for the sand holes at the base of the rock which the sharks have dug to make their home. Juvenile Oriental sweetlips can be seen performing their unusual dance. Indian, orange-lined and titan triggerfish are all around here too as well as cuttlefish.

Closer in towards the main island is another long narrow swim-through. Grouper and emperor angelfish can be seen here. Look up towards the surface to see crocodile long-toms swimming above.

Bida Nai Reef Basics: Staghorn reef and wall diving
Depth: 5 - 30m
Visibility: 10 - 20m
Currents: Gentle
Surface conditions: Can be choppy
Water temperature: 27 - 30°C
Experience level: Beginner - intermediate
Number of dive sites: 1
Diving season: All year round
Distance: ~45 km east of Phuket (3 hours), 30 km southwest of Krabi (2½ hours)
Access: Phi Phi scuba daytrips and liveaboards

• Koh Phi Phi travel information

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