ROSS River virus has been found in Gippsland Lakes and 90 Mile Beach mosquitoes.
The state Health Department is urging people to protect themselves against mosquito-borne diseases such as Ross River and Barmah Forest viruses.
Recent weather conditions are favourable to mosquitoes and mosquito breeding.
All parts of Victoria where there are mosquitoes may carry a risk for Ross River virus infection, although the risk is greatest in rural and regional Victoria.
Ross River and Barmah Forest viruses disease are similar. Both can cause joint swelling and pain, fatigue and muscle aches which can persist for many months, while a rash and fever may also develop.
It takes three to nine days for symptoms of Ross River virus disease to occur after exposure, and occasionally up to 21 days.
Barmah Forest virus disease symptoms occur between seven to 10 days after a sting from an infected mosquito.
While people recover from the initial onset, symptoms may recur in some individuals for more than a year or longer.
The best protection from these diseases is to avoid mosquito stings.