Tiny insects are being enlisted in the fight to control an invasive aquatic weed that is clogging up parts of Wappa Dam.

Salvinia – a free-floating aquatic plant – has invaded at least a third of the drinking water supply dam, located west of Yandina in the Sunshine Coast hinterland.

The non-native weed forms thick mats that can quickly cover water storage areas, degrading water quality and impacting wildlife habitat. 

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

Salvinia - a free-floating aquatic plant - has invaded parts of Wappa Dam.

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,” Mr Searle 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.” 

Seqwater is treating salvinia-infested areas by releasing weevils which feed on the invasive plant

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.”

No water-based activities are permitted at Wappa Dam. 

Seqwater’s weed management will not affect the dam’s ability to supply water or recreational facilities. 

Mr Searle said, as with all biological controls, the method would not eradicate salvinia but it is expected to significantly reduce the biomass within the next eight weeks.

Close-up view of the salvinia weevil