Mannum's main street has closed because of flooding just as the River Murray has reached its peak flow through the town in South Australia's Murraylands.

The State Emergency Service (SES) says the peak water level past Mannum was reached on Saturday.

The river level in Mannum topped out at about 2.5 metres higher than normal.

The SES has closed much of Mannum's main street, Randell Street, due to water coming up through a stormwater pipe on the dry side of the Murraylands town's main levee.

Work is underway to fix it, including pumping it back into the river and sending divers in to try to block the seepage.

Behind the barricade is Alicia Wegener's takeaway shop that she has now had to close.

She was hoping the road would be open at least for the weekend trade, but instead she has donated her supplies to the Mannum flood relief centre.

"We had deliveries come yesterday … a lot of stuff we can freeze and salvage, otherwise a lot of the fresh stuff we decided to donate to the Lions Club up at the relief centre and hopefully they can use that," she said.

She said she had "no idea" when she would be able to reopen her business, but hoped it would only be a "couple of weeks".

"Fingers crossed our power stays on and then when we come back we can start up again without losing too much," she said.

Stress for homeowners

The town's levee has been holding up so far, but it was built to protect homes and businesses only on the higher side of the main street.

Don Grant's home lies on the wrong side of the levee and he has not been able to stay there for more than a month.

He said the water level was probably over the top of the sandbags he and his wife Maria had put around their property.

"We put like 2,500 sandbags around the house, but it looks like the sandbags at the front on the river side may have collapsed," he said.

"So that's going to allow inundation into the house and we've just got to deal with it."

Mr Grant said it was "a little bit hard" to watch.

"I was pretty stressed when it was first happening, but now I'm probably a little more relaxed, come to terms with the reality of the whole situation," he said.

Once the water levels drop, attention will turn to the lengthy recovery process.

"We probably won't be back in our property probably until about March by the time the water goes down," Mr Grant said.

"And then we've got to start to clean up."

The peak is expected to reach Murray Bridge, Jervois and Wellington in coming days and then the Lower Lakes after that.

Sandbags are available from the Bowhill Community Centre, the Goolwa Football Club, the Mannum Football Club, the Milang Football Club and the Murray Bridge Showgrounds.

Lake Bonney reopened

Lake Bonney has reopened to swimming and other water activities after being closed since late December due to harmful levels of blue-green algae detected in the water.

The algae appeared after the SES cut off its connection with the Murray in an effort to prevent properties becoming inundated and to protect wastewater infrastructure in Barmera. 

SA Health says the most recent samples of the lake, taken yesterday, showed the water was safe, but it would continue to monitor algae levels.