The sewage was discharged four times last year from west Hull pumping station and once so far this year.
Yorkshire Water says the pumps are only put into action in extreme weather to help prevent flooding and says torrential rain was responsible for the last discharge.
But John Goodman, of Cottingham Flood Action Group, believes Yorkshire Water should do more to protect the environment – particularly given news of the E.coli outbreak in Europe – and feels there should also be tougher regulation by the Environment Agency.
Mr Goodman said he thought the use of pumps was down to simple expediency. “We believe the maximum rainfall in a 24-hour period in the past 15 months has been little more than a one in two year storm, not more than 30mm. Yet the system they have in place, the Humbercare system, which treats sewage at Saltend, is supposed to cope with a one in 30 year storm. It should easily cope with this amount of water.
“Humbercare was supposed to prevent the pumping of raw sewage into the Humber, patently it is not doing so. It’s a health risk and the EA should be working with YW to prevent future pumping.”
The giant pumps were installed after Yorkshire Water was severely criticised following the deluge in 2007, which inundated 8,000 homes.
In a statement Yorkshire Water said: “We take our environmental responsibilities seriously and the pumps at our east and west Hull pumping stations only operate during times of extreme weather when there is too much surface water in the sewerage system because of excess rainfall.
“When operating under these circumstances, the pumps discharge heavily diluted excess waste water into the Humber Estuary to help prevent flooding in the city. Because the pumps operate in emergency situations to help prevent flooding, the Environment Agency grants us an emergency consent to do so.
“In Hull since 2008, we have spent over £30m to ensure that our assets in the area are as robust and resilient as possible.
“And we are currently undertaking a comprehensive study of our network to make sure we fully understand all its interactions with surface water and other water courses.”
No one was available to comment from the Environment Agency.