The warning is just a formality for managers of holiday parks, including the Great Aussie Holiday Park at Bowna, who say there have been signs of algae for weeks.

"We have had a very different start to the year than we are normally used to," manager Belinda Van Dyck said.

"First the bushfires came and we saw a lot of cancellations, although we did have an increase in people coming who had been evacuated.

"And of course the water is so low at the moment we haven't been able to get boats in our boat ramp because there is just no water.

"Some people have had their boats damaged because of the low water level.

"And now the algae, it is just another blow really."

Ms Van Dyck said the park had made the option of telling holiday-goers to not use the water for the past few weeks.

"We have been seeing it get worse and we just made the decision to inform our guests to be aware of it," she said.

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"It is a bit disappointing we are now looking at more cancellations especially with the Victorian long-weekend coming up and of course the big Easter break.

"We are booked out for Easter and it is hard for us to inform guests if the water will be usable by then.

"We just don't know.

"A lot of people come here to utilise the water, but it is out of action."

The lake is only sitting at 17.11 per cent.

Ms Van Dyck said the low levels have had an impact on tourism.

"We aren't as full as we normally are for this time of year with people who ski and fish.

"Hopefully the algae goes away soon and the lake can be utilised again."

Other lake-side businesses including Lake Hume Resort and Lake Hume Tourist Park were contacted for comment, but did not return phone calls yesterday.

Border lake-goers also expressed their concern on Facebook after the alert was issued, saying they too have seen evidence of algae on the water.

Regular monitoring will continue and the alert will be lifted as soon as the high levels of algae dissipate.

In 2019, a red alert was in place for Lake Hume for 19 days.