Pumps in the lower Kaituna River have been going "flat tack", Mr Blackwood said.
The Okere gates have been open for two weeks and were discharging flood water from Lakes Rotoiti and Rotorua at capacity, he said.
"There are no further steps we can take to lower these lake levels and residents should expect some flooding around lake margins."
Mr Blackwood said the flood management team was working with MetService meteorologists around what else the severe weather warning would mean.
Western Bay of Plenty District Council has urged residents to make sure they were prepared for as much as 250mm of rain to fall between Wednesday and Friday.
People have been advised to clear gutters and stormwater grates of any debris, have an evacuation plan in place - including for pets - and have a supply of food and water.
People should also avoid areas where there have been recent slips as the ground might still be unstable.
Council staff and contractors were preparing roads and utilities for the incoming weather and would be monitoring and responding to issues throughout the week.