Lake Eppalock and Cairn Curran Reservoir are still subject to blue-green algae warnings, with high levels of the algae detected at both popular recreational areas.
People are advised to avoid contact with the water at both locations.
Goulburn-Murray Water says the warnings will remain in place until at least January 12.
Water quality co-ordinator Bianca Atley said the two water storages were last tested last Wednesday and a visual inspection was carried out on Friday.
Ms Atley said the high levels of algae present in the water meant the blooms would not adequately clear until at least the end of next week, although they might remain present for longer.
Both bodies of water have experienced high levels of blue-green algae since mid-December.
Blue-green algae contain toxins that can cause rashes, itchiness, asthma, numbness of lips and limbs, nausea, vomiting, diarrhoea, and sore eyes, ears and nose.
People should not eat any mussels, yabbies or crayfish from algae-affected areas, and watering of edible plants using the water should be avoided.
Ms Atley said it was not possible to predict how long blooms would last: some cleared after two weeks, while there had been blooms that lasted 541 days.
But the presence of the algae has not stopped people from enjoying the surrounds of Lake Eppalock.
While some people cancelled their plans to spend holiday time at the lake, two caravan parks were largely booked out over the festive period.
Ms Atley said testing and inspections of Lake Eppalock and Cairn Curran Reservoir would continue at least weekly until the warnings were lifted.
She said GM Water carried out testing at major storages at least fortnightly in summer, when the warmer weather was more likely to result in blooms. Blue-green algae occur naturally and use sunlight to grow.
For updates on blue-green algae, including unaffected lakes, visit www.g-mwater.com.au/news/bga.