Tests are being done to find out who dumped a large amount of waste at Whanganui's waste water treatment plant, creating a severe stench in parts of the city.
Mayor Annette Main said the facility is struggling to process the volume that is coming in.
The plant was built in 2005 but is not working properly and is emitting a strong hydrogen sulphide-odour.
Ms Main told Summer Report she wants to know why the plant is not operating properly and what can be done to fix it.
