Pulling the plug on Salvinia

Published on 12 December 2022

Flatrock Dam - salvinia weed

Shoalhaven Water will soon lower the water level at Flatrock Dam to eliminate the spread of a problematic floating aquatic weed, called Salvinia (Salvinia molesta), in the reservoir.

Salvina is a fast-growing aquatic weed that can cause significant problems in dams by reducing food and habitat for fish and other aquatic animals, as well as water quality.

The weed is difficult to control even in good conditions. Past measures to treat the weed using biological control by the Salvinia weevil (Cyrtobagous salviniae) have been unsuccessful.

Salvinia does not produce seed and reproduces from fragments. To eliminate the plant, there can be no living fragments that can come into contact with the water.

Shoalhaven City Council’s Manager - Environmental Services, Dr Michael Roberts said the weed is of national significance and urgent action to lower the water level is required to eliminate the potential spread.

“Salvina can create a thick blanket across a water body which causes water quality problems and prevents recreational use of our waterways. Eliminating the weed is also imperative due to the proximity to the Bamarang town water supply”, Dr Roberts stated.

Lowering the water level is part of Council's ongoing control of Salvinia at Flatrock Dam, in association with direct control of the weed using approved control methods.

The water level may be kept low for an extended amount of time depending on the weather over the summer period, to allow all Salvinia in the vegetation around the edge of the dam to dry out and die.

Flatrock Dam is no longer part of Shoalhaven Water’s supply system and is used for recreational activities such as swimming and fishing. It is currently closed to the public until further notice.

Shoalhaven Water along with Shoalhaven City Council’s Biosecurity staff will monitor the situation over summer and adapt management techniques, depending on the weather.

For more information about the Salvinia weed visit the NSW Department of Primary Industries website.

Image: Salvinia weed growing on the water surface at Flatrock Dam



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