The Central Hawke's Bay District Council is under the pump to modify its wastewater treatment plant and quickly.

Serious concerns have been raised about the new $6 million plant.

Despite the recent upgrade, it's still releasing harmful bacteria and wastewater into the Tukituki River at unacceptable levels.

Hawke's Bay Regional Council spokesman Iain Maxwell says a clear plan is needed from Central Hawke's Bay District Council to how it intends to fix the problem.

He says meeting the discharge standards is non-negotiable.