The Boston-area COVID wastewater tracker data keeps on rising, sending out alerts to the public that “a new wave has begun,” according to a leading local epidemiologist.

The latest update from the coronavirus wastewater tracker reveals that COVID levels are back up to the measurements from early February. This jump comes as the omicron BA.2 variant takes hold, while mask mandates have been lifted.

The wastewater data in both the south and north of Boston regions hit lows at the start of March. Now, the average levels in both regions are well more than double the low marks. The sewage data is the earliest sign of future virus cases in the community.

“I think it’s getting pretty clear that a new wave has begun and we will start to see more of a jump in the case numbers soon — more than we are already seeing,” said Matthew Fox, a Boston University School of Public Health epidemiology professor.

“The wastewater data has been a reliable predictor so far so I think we can rely on it here,” he added.

The north of Boston’s COVID wastewater average has increased 160% since the very low level about three weeks ago. The south of Boston’s average has gone up 146% since the start of March. The wastewater levels are still far below the omicron peak.

One-day measurements in both the north and south regions during the past week are back up to the levels from the first week of February.

“The gradual upward trend in the wastewater is worrisome,” said Davidson Hamer, a Boston University School of Public Health infectious diseases specialist. “The good news is that it has been a slow upward trend.

“I suspect that it’s a combination of greater spread of BA.2, reduced mask use in public places, and people who have been cautious starting to let down their guard,” he added. “Hospitalization numbers have not increased much which is good.”

The BA.2 variant is now the dominant strain in the U.S., and cases have been rising in Massachusetts over the last few weeks.

This omicron subvariant wave is not expected to surge like the omicron wave in December and January, but people should be ready to start masking again in public places and reduce their interactions, Fox said.

“As for what we should do, we should take precautions and wait and see how bad this wave is,” he said. “My guess is it won’t be as bad as previous waves — in terms of severe illness — but we should be prepared to take action should things get worse.”

Hamer said he feels there’s no need to reinstate a mandate for indoor mask use in public places, but “older people and those with weak immune systems need to continue to be extra careful.”

He added that anyone with symptoms consistent with COVID should do a rapid test or even two over consecutive days before having contact with family, friends, schoolmates or work colleagues.