Lake Hume has now joined the list of waterbodies in the region with a red alert level warning for blue-green algae.
Water NSW issued the alert on Monday afternoon.
"Water quality monitoring by WaterNSW indicates the presence of high levels of potentially toxic cyanobacteria," the statement said.
"Additionally, visual observations have identified surface scums across large areas of the waterbody.
"A red alert level warning indicates that people should not undertake recreational activities where they may be coming into direct contact with the water. Contact with the water may also pose a threat to livestock, and pets.
"The dominant cyanobacteria detected are known to be toxin producers and may produce a strong musty odour.
"People are advised not to enter the water, not to drink untreated water or bathe in untreated water while a red alert level warning is in place. Boiling the water will not remove algal toxins.
"People should not eat, fish, mussels or crayfish from red alert warning areas."
The alert is listed on the WaterNSW map at the dam wall, Lake Hume Resort, Heywoods, and at Ebden on the Victorian side, however the alert is relevant for the entire dam.
The dam is at just 17 per cent capacity.
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Regular monitoring will continue, and the alert will be lifted as soon as the high levels of algae dissipate.
Blue-green algae occur naturally and can reproduce quickly in favourable conditions where there is still or slow-flowing water, abundant sunlight and sufficient levels of nutrients.
It is not possible to predict how long the algae will remain at high levels.
Updates about blue-green algae blooms and red level warning areas can be obtained by calling 1800 999 457 or visiting www.waternsw.com.au/water-quality/algae.