Sediment-carrying rivers have been diverted, sea level has risen (increasing the volume of water in the lagoon), a deep-water channel has been dredged for shipping, and turbid waters are killing the eel grass that stabilises mud flats.

ECONOMIST: Flood barriers

Boats chug through the channels, with the lagoon waters running from milky greens to deep blues.

BBC: The price of protecting paradise in Palau

At the new Intercontinental Hotels resort at Bora Bora, air conditioning for its 80 villas on a pristine lagoon comes from a system of pipes extending 1.5 miles offshore and 3, 000 feet deep, tapping the cooling power of 41-degree seawater.

FORBES: Fort Knox's Buried Treasure