South Australian authorities are warning the public to be on alert after an increase in the number of cases of mosquito-borne viruses being detected in people and mosquitoes.
Twenty-eight virus detections have been made in mosquitoes used to warn of possible human cases, compared with three last year.
SA Health has been notified of 38 cases of mosquito-borne diseases in South Australians this season, including one man who caught Japanese encephalitis virus (JEV).
Most of the other other cases have been of Ross River virus, while three cases of Barmah Forest virus have been diagnosed.
Murray Valley encephalitis, JEV and and West Nile virus in particular can be fatal because they can cause brain swelling.
Chief Public Health Officer Nicola Spurrier said a hot summer after a cold, wet spring and the Riverland flooding had combined to create a big mosquito season.
"This year, I am really concerned," she said.
"I think it's potentially going to be the worst season that we've had in South Australia, now with this new virus JEV on top of the other viruses.
"However, if everybody took these precautions and we had a lot of people out there putting on their repellent and putting on long-sleeve shirts and such-like, it's possible that we won't have so many cases this year."
Ross River and Barmah Forest virus symptoms include fever, headache, muscle ache and pain and joint inflammation.
Murray Valley encephalitis, JEV and West Nile can have the same symptoms, as well as confusion and neck stiffness, followed by patients going into a coma.
Warning over blue-green algae
SA Health is also warning against swimming at the southern end of Lake Bonney, in the Riverland, after another flare-up of blue-green algae .
The lake was reopened for water activities on Saturday. However, SA Health has now warned against swimming between the Barmera jetty and the Lake Bonney Yacht Club.
Blue-green algae has reappeared in that section of the lake despite testing on Saturday showing the water was safe to use.
SA Health principal water quality adviser David Cunliffe said algae had increased along the Barmera foreshore despite mitigation efforts.
He said direct contact could cause skin irritation, and swallowing water with algae in it could make people sick.
"Anyone who has been swimming at Lake Bonney should closely monitor for symptoms – especially in children and pets," Dr Cunliffe said.
"These symptoms can include nausea, diarrhoea, vomiting and abdominal cramps."
The algae appeared last month after the State Emergency Service (SES) used a levee to block off flows from the River Murray into the lake to prevent properties being inundated and to protect wastewater infrastructure in Barmera.
The Berri Barmera Council says works to reconnect Lake Bonney with the River Murray will commence as soon as river levels have sufficiently fallen.
River height measurements taken yesterday show the river is approximately 2.1 metres higher than Lake Bonney.
It is expected the river will need to drop at least 1m before work to reopen the inlet can begin.
Highway may become flooded
The state government is warning that the Princes Highway may be inundated between Tailem Bend and Meningie, along Lake Albert.
The speed limit on the road has been cut to 60 kilometres per hour.
"It could cause about an hour detour, which is suboptimal, but we'll lower the speed limit, see how close the inundation gets to the road, whether it's safe to use," Transport Minister Tom Koutsantonis said.
"We might conduct convoys — that is, managed passings."
