October 3, 2014, 4:52 pm

Pumping raw sewerage into the ocean was a source of elevated levels E. coli bacteria that closed Darwin's beaches four years ago, a university study has found.

The sewerage outfall known locally as the "poo shooter" at Larrakeyah beach, about 2 kilometres from Darwin's centre, pumped raw sewerage into the ocean for 47 years.

It was pumping about 1.5 billion litres of sewerage a year before it was closed in 2011.

Charles Darwin University professor Karen Gibb led a team of researches gathering and studying water samples from across Darwin.

The team established a link between the sewerage outflow and elevated levels of E. coli at Doctors Gully and Lameroo beaches in the 2010 dry season. That year Darwin was forced to close all its beaches because of the toxic bacteria.

But she said questions still remained about what caused E. coli levels at other beaches to soar.

"In our environment where we have a lot of animals, a lot of things happening, lot of movement of tides and sediment there'll be a huge amount of E. coli in the system anyway," she said.

"We should actually be looking at a whole range of other indicators including pathogens to really get a good sense of risk and what actually matters to our recreational waters.

"Rapid Creek is one of several beaches were there was no single source causing the E. coli.

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'Poo shooter' sewerage pipe to blame for toxic E. coli that closed Darwin beaches, study finds