Residents along the Georges River are being advised to avoid all contact with the river for at least another three days as crews continue to clean up after a major spill of sewage last weekend.

NSW Health extended an alert in place since the weekend for people and their pets to avoid the river from Macquarie Fields all the way downstream to Botany Bay. Swimming, sailing, canoeing and fishing are also to be avoided.

A heavy downpour on Friday night submerged a pumping station at the Glenfield Wastewater Treatment Plant, resulting in the emergency release of 150 million litres of ‘‘heavy diluted but untreated’’ waste water into the river, Sydney Water said.

Sydney Water continues to test the river for contamination at 10 sites downstream of the plant. It has also deployed teams to clean the riverbank at ‘‘multiple locations’’ and is working three aerators in the river to maintain oxygen levels.

‘‘The primary contamination is around the Liverpool Weir and that’s where we’ve placed the aerators,’’ said Emma Whale, a spokeswoman for Sydney Water.

Water quality testers have also found a ‘‘slight reading’’ of contamination near the Chipping Norton stretch of the river, Ms Whale said.

Earlier in the week, Sydney Health warned that the water in the river is likely to pose a ‘‘serious risk of gut and skin infections,” and advised people coming into contact with it to “wash themselves carefully” and seek medical advice if they had any open wounds that might have been exposed.

Residents are advised to visit the Sydney Water website for further updates.