TINY insects are being used to fight an invasive aquatic weed clogging up parts of a Sunshine Coast Dam. 

Salvinia - a free-floating aquatic plant - has invaded at least a third of the drinking water supply at Wappa Dam, west of Yandina, forming thick mats that can degrade water quality and impact wildlife habitat.

Seqwater biosecurity officer Geoff Searle said an exceptionally warm winter had created ideal conditions for the weed to flourish.

In an effort to rein in the plant, Seqwater has unleashed tick-size weevils, which live and feed aggressively on salvinia.

Mr Searle said the weevils were a good biological control option.

"The weevil larvae feed on new growth buds and tunnel into the stem and roots of the plant," he said.

"If they eat enough, the plant sinks.

"In the initial stages of weevil damage, some salvinia leaves will turn brown.

"As the weevils continue their control efforts, the whole mat will turn brown, sink and decompose."

For the past few weeks, Seqwater has been adding weevil-infected salvinia to the infested areas of Wappa Dam.

Floating containment booms are also being used to limit the spread of the infestation.

"Controlling aquatic weeds like salvinia and water hyacinth is an ongoing battle but if left uncontrolled, it can have significant environmental and economic impacts," Mr Searle said.

"We've used weevils as a biological control option to treat weed infestations in other Seqwater-managed drinking water storages and it has proven effective."

ABOUT SALVINIA

• Salvinia molesta is a restricted invasive plant under the Biosecurity Act 2014. It must not be given away, sold, or released into the environment without a permit.
• Salvinia is a free-floating, green-brown, freshwater plant with branching horizontal stems and has submerged feathery 'roots'. It can easily break apart and it can also form dense mats of foliage on the water surface.
• This plant reproduces vegetatively, with the floating branches readily breaking apart and forming new plants.
• There are several species of salvinia that occur naturally in America, Europe and Asia. So far, only one species- Salvinia molesta (a native of Brazil)-has become established in Queensland.
• Salvinia is mainly spread by people who empty aquariums and ponds into waterways.