An independent inquiry into the failing riverbanks in Edgecumbe has found no sole reason for the flooding, and even lowering the lake level wouldn't have prevented the disaster.
It also says residents "were insufficiently aware" of the risks that came with living in the flood-prone township.
About 1600 people were evacuated from the Bay of Plenty town in April when the Rangitaiki River burst through the stopbank, destroying 15 homes and damaging 250 more.
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After six months of waiting, residents hoped the report commissioned by the Bay of Plenty Regional Council could provide answers about how the flood occurred and who is to blame.
But the findings, presented on Tuesday by Sir Michael Cullen, cites multiple reasons for the flood.
It was found the April flood was caused by water escaping through the foundations of the floodwall, causing it to give way from pressure rising in the ground.
But the report also suggests the lake levels were managed as best as they could be, and lowering it any further would have had little impact.
"Damage to the wall foundations during the 1987 earthquake may have also been a contributing factor," Sir Michael said.
"We have also found that the fact that Reid's Floodway and Spillway were not completed meant that it was unable to play a substantial role in diverting floodwater away from Edgecumbe. If the upgrade had been completed, it would have reduced the pressure on the floodwall and may have prevented the failure.
"It also appears that many of the residents of Edgecumbe, for whatever reasons, were insufficiently aware of the risks of serious flooding in the township."
Some residents are still homeless as they wait for repairs to be completed.