Queensland has had its highest number of Ross River virus cases in 20 years but the outbreak is now in decline.

The worst Ross River virus outbreak in Queensland in 20 years is in decline, the state's health authority says.

There have been more than 4500 cases of the virus across the state this year - more than five times the annual average.

The majority of cases have been in southeast Queensland where breeding conditions have been ideal for mosquitoes after excess rainfall.

Queensland Health Senior Director Sonya Bennett said cases of the mosquito-borne virus peaked in February.

Dr Bennett said there were now about 80 infections a week, but expected this to drop significantly as temperatures cooled.

"With the recent wet weather and the increase in mosquitoes we may see a small surge in cases, but I don't expect that will be another outbreak as such," she said.

Symptoms of Ross River fever include painful or swollen joints, sore muscles, skin rashes, fever, fatigue and headaches.

Most people recover within two weeks, but it can take up to six to be back to full health.

There's no known cure.

Dr Bennett urged southeast Queenslanders to cover-up and avoid being outside at dusk and dawn, when mosquitoes were biting, and to control mosquito breeding around homes by emptying water from containers.