Ban on boating eased on flooded Murray

Restrictions along part of the Murray River are being lifted for the first time since the flood emergency began but swimming is still not permitted in popular holiday areas.

From Wednesday afternoon, boats were allowed on the water from the South Australian border with Victoria to Barmera, in the state's east.

All motorised vessels, including jet skis, must stick to strict speed limits. Vessels may only travel up to 10 knots during the day and four knots at night or near levees.

Recreational fishing has also been given the green light but water skiing and swimming remain banned.

There are no changes to rules regarding kayaks and house boats.

Premier Peter Malinauskas said it was the first sign South Australia was moving into the next stage of the flood emergency.

"People can now go out in the water in their dinghy, throw a line and do some yabbying," Mr Malinauskas told reporters in Mannum, east of Adelaide.

"Just make sure that you observe some basic rules when it comes to personal safety."

Police Commissioner Grant Stevens said holiday-makers needed to be cautious on the river and speeds limits were in place because boats were unlikely to tip over if they collided while travelling slowly.

"There is a higher risk level at the moment because of the fact that there's so much material in the river, so we have to be careful," he said.

It's estimated about 4000 properties have been flooded to some degree since the natural disaster reached the state, including about 400 primary residences.

Meanwhile, Murray Valley encephalitis virus has been detected in mosquitoes in five council areas along the river.

No cases have been detected in humans but authorities warn there is "very real risk" a person could be infected with the incurable disease.