Papua New Guinea depends heavily on its waterways, for drinking, fishing, farming and transport to schools.

And if the waterways become clogged, it can bring hardship, and in a medical emergency, even cause death.

This is where the water hyacinth comes into the story.

Brought in from South America as a decorative plant, the Water Hyacinth has been spreading its way through all provinces of the country. It is hardy, quick growing and seeds can remain alive in the mud of a lagoon for up to 17 years, clogging waterways that eventually become impenetrable.

When CSIRO scientists were asked to help, they already knew that pesticides would be ecologically disastrous, uneconomical and only have a short term effect. The only solution was to find a natural biological enemy.

Surveys in South America had found several species of weevil that would eat only Water Hyacinth and not harm any other plants. In fact these weevils were so choosy that they would rather die than eat anything else.

Water Hyacinth weevils lay their eggs on the stems and leaves of the weed. They hatch into grubs that munch on the inside of the stems. Then, after resting in a cocoon for several weeks, they appear as fully grown weevils to feast some more on the leaves.

Over a number of seasons the plant becomes water-logged and eventually dies.

Now this weevil is gobbling its way through the Water Hyacinth problem and helping clear the waterways of Papua New Guinea.