Oilsands giant Suncor says there was no bitumen in wastewater that leaked from a burst pipe earlier this week.

An email from the company late Wednesday says 350,000 litres of wastewater leaked into the Athabasca River for about 10 hours.

"As soon as we realized there was a discharge into the river, work immediately began to stop the flow," said the email from Suncor spokeswoman Sneh Seetal.

"Our tests confirm the process affected water was a combination of water with suspended solids (clays and fine particulates) and inorganic and organic compounds. It does not contain bitumen.

"This process affected water was mixed with treated water, prior to entering the river. The ratio was approximately six parts treated water to one part process affected water."

The company says it has hired a third party to determine the impact of the wastewater entering the river, but adds according to its calculations, it likely had a "short term, negligible impact on the river."

Suncor also called the release of wastewater into the river "unacceptable.

"Water quality is an important issue for us, the community and is of paramount concern to our neighbouring stakeholders. As a precautionary measure, we are continuing to take water samples at various downstream locations along the river."

When Suncor first publicly acknowledged the spill on Tuesday, it said it didn't know exactly what was in the wastewater or how much of it spilled at its base plant north of Fort McMurray.

Earlier Wednesday, 11 groups said they were sending a letter to the Alberta government about their concerns over the leak.

"This is all information that Suncor and the Alberta government should know and be immediate public knowledge, but we remain in the dark," said the letter dated Wednesday.

"We hereby demand the immediate release of this information, including pictures, so Albertans can judge for themselves the impact of this spill."

Greenpeace, the Sierra Club, the Council of Canadians, First Nations, and Forest Ethics Advocacy are among the groups that signed the letter that was addressed to Alberta Environment Minister Diana McQueen.

A department spokesman said she was in Calgary on Wednesday and hadn't yet received the document.

Suncor's Seetal said Tuesday that the pipe, about four metres long and 10 centimetres wide, froze and burst, sending "process-affected water" into a partially-frozen outfall pond containing treated water.

Some of the fluid then entered an approved discharge area containing clean water, and was released into the Athabasca River.

Wayne Wood said government crews were still at the site, working with Suncor and overseeing cleanup and containment.

He said the government is still waiting for test results from water samples taken from the spill site and the river.