Reefwander
Dark blue open water seen from an aircraft wing, with the low hills of the Florida Islands lining the horizon under cumulus clouds — Iron Bottom Sound

Coral Triangle · Solomon Islands

Iron Bottom Sound

Wade off a Honiara roadside onto a Japanese transport from 1942

Photo: Jenny Scott from Adelaide, Australia · CC BY 2.0

The water between Guadalcanal and the Florida Islands took more than fifty warships and hundreds of aircraft during the Guadalcanal campaign, and Allied sailors named it for what was on the bottom. Most of the warships lie past a thousand metres and will never be dived, but the transports driven ashore are within reach: Bonegi I and II are shore dives from a Honiara roadside, and the Florida Islands add clear-water reef and the twin chimneys of Twin Tunnels.

About diving in Iron Bottom Sound

Diving here is lower-key than the history suggests. Operators are based in the capital, and a wreck day usually means a van ride out along the coast road west of town, kit assembled on the sand and a walk into the water, with tanks swapped in the shade between dives and no boat involved. The land behind the entry points is customarily owned and a small fee is normally collected at the beach, which is one reason most divers arrange the day through a centre. Boat days point north instead, across the sound, and depend on what the crossing looks like that morning.

The two halves of the area have little in common. The beached transports lie bow-up on the slope with their sterns running away downhill, so depth is chosen simply by how far out you swim; the shallow ends are bright and crusted with growth, while the deeper sections fade into silt and low light, more so after heavy rain. The Florida Islands are a different proposition: hard reef structure, drop-offs and swim-throughs, and visibility the shore sites rarely match.

The signature dive is a slow swim along a hull that has been on the bottom since 1942, ordinary fittings now under coral growth, clouds of small fish moving through the frames and the shoreline visible above you the whole way. Night dives on the shallow plating are a local staple. Technical divers work the deeper wrecks around Tulagi, which sit well past recreational limits and rarely figure in a visiting diver's plans.

It suits people who come for the story as much as the fish. Visibility is modest by regional standards, the topside is a working capital rather than a resort strip, and this is not a polished dive holiday. Most divers treat it as two or three days attached to a longer trip further west, which is the sensible shape: time for the shore wrecks, one crossing to the reefs, and the campaign's land sites — ridges, airfield, memorials — in between.

Best time to dive Iron Bottom Sound

Iron Bottom Sound season rating, sea surface temperature, daytime high and rainfall by month, 2011–2025 averages
JanFebMarAprMayJunJulAugSepOctNovDec
SeasonFairFairGoodPrimePrimePrimeGoodGoodGoodPrimePrimeGood
Sea surface30°C86°F30°C86°F30°C86°F30°C86°F30°C86°F29°C84°F29°C84°F29°C84°F29°C84°F29°C84°F30°C86°F30°C86°F
Daytime high30°C86°F30°C86°F30°C86°F30°C86°F30°C86°F30°C86°F30°C86°F30°C86°F30°C86°F30°C86°F31°C88°F30°C86°F
Rain303 mm11.9 in311 mm12.2 in280 mm11.0 in225 mm8.9 in241 mm9.5 in206 mm8.1 in205 mm8.1 in195 mm7.7 in193 mm7.6 in179 mm7.0 in199 mm7.8 in274 mm10.8 in
Iron Bottom Sound season rating, sea surface temperature, daytime high and rainfall by month, January to June, 2011–2025 averages
JanFebMarAprMayJun
FairFairGoodPrimePrimePrime
Sea surface
30°C86°F30°C86°F30°C86°F30°C86°F30°C86°F29°C84°F
Daytime high
30°C86°F30°C86°F30°C86°F30°C86°F30°C86°F30°C86°F
Rain
303 mm11.9 in311 mm12.2 in280 mm11.0 in225 mm8.9 in241 mm9.5 in206 mm8.1 in
Iron Bottom Sound season rating, sea surface temperature, daytime high and rainfall by month, July to December, 2011–2025 averages
JulAugSepOctNovDec
GoodGoodGoodPrimePrimeGood
Sea surface
29°C84°F29°C84°F29°C84°F29°C84°F30°C86°F30°C86°F
Daytime high
30°C86°F30°C86°F30°C86°F30°C86°F31°C88°F30°C86°F
Rain
205 mm8.1 in195 mm7.7 in193 mm7.6 in179 mm7.0 in199 mm7.8 in274 mm10.8 in

2011–2025 averages. Sea surface: NOAA Coral Reef Watch, measured at the surface, so deeper water can run colder. Daytime high and rain: NASA POWER.

Apr–Jun and Oct–Dec are calmest; the Jan–Mar wet season brings runoff that cuts visibility on the shore wrecks.

Best months: April, May, June, October, November

Iron Bottom Sound water temperature and weather by month

The sea surface stays between 29 and 30 °C (84–86 °F) all year. Rain falls through the year, about 230 mm (9.1 in) a month on average, with February the wettest. Daytime highs sit around 30 °C (86 °F) all year. The coldest water here is about 28 °C (82 °F), so pack a 3 mm, or even a 2 mm, suit.

Dive types & marine life

The hulls carry dense clouds of small reef fish, grouper holding in the shadowed sections and barracuda off the deeper wreckage, while nudibranchs and small critters make the shallow plating a good night dive. Turtles are more likely over the Florida Islands reefs. April to June and October to November are the clearest months; wet-season runoff dulls the shore sites.

  • Wreck
  • Reef
  • Night
  • Muck & macro
  • Cave & cavern
  • Reef fish swarms
  • Macro critters
  • Nudibranchs
  • Sea turtles
  • Groupers
  • Barracuda

Best dive sites in Iron Bottom Sound

A 155 m Japanese transport you reach by walking off the beach

to 55 mintermediate

A 133 m transport whose engine still breaks the surface

to 27 mintermediate

Pinnacle

Two lava tubes through the reef top, exiting in a cave at 35 m

12–45 m · max 60 madvanced

A US attack transport in 35 to 60 m, open to penetration

35–60 madvanced

How to get to Iron Bottom Sound

Honiara is the country's international gateway and the base for everything here. Town centres run transport west along the coast road to the shore wrecks and boats north across the sound to the Florida Islands, weather permitting. Passenger boats also cross to Tulagi for divers who would rather stay nearer the reefs.

Photos from Iron Bottom Sound

  • U.S. Navy, photo was taken from USS San Juan (CL-54). · Public domain

  • Unknown author · Public domain

Dive videos

Diving WWII Wrecks in Solomon Islands | What We Found Underwater · Dive Wise on YouTube

WRECKED in the Iron Bottom Sound (Expedition Drenched S1 Ep. 67) · Expedition Drenched on YouTube

Photo credits

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