A public health warning is still in place for Lake Rotorua near Arnold St and Waiteti Rd in Ngongotahā, Rotorua Lakes Council says.
The initial warning was issued on Tuesday after a wastewater spill.
In a social media update on Wednesday, the council said test results from the day of the overflow and the next day had been analysed.
"As expected, the highest levels of contamination were detected at the entry site of the overflow into the lake, and testing shows that the levels of contamination reduced significantly within the first 12 hours.
"Test analysis takes at least 24 hours and we expect more results to be available tomorrow," the statement said.
Investigations into the cause of the computer fault (the loss of programming code) were still ongoing.
TRILITY would continue testing to determine when the warning should be lifted.
Forty-eight hours was the generally advised minimum time for such warnings to be in place and test results would confirm the warning time frame, the statement said.
In the meantime, it was safe to enter the water at other locations around the lake. The council advised people to look for signs that may indicate a health warning.