While a human crisis was unfolding on the Calder on Tuesday morning, an ecological crisis was happening beneath it.

The accident couldn't have been in a much worse place.

Directly underneath the section of the Calder where the truck flipped runs Steele Creek, a narrow trickle surrounded by tranquil parkland.

About 20,000 litres of unleaded fuel and diesel, plus more firefighting foam, was emptied into that creek via drains on the side of the road during the course of the accident.

There was enough fuel in the river to make some parts of it hazardous to human health, firefighters said.

The part of the creek nearest the road has been blocked off because the fumes are too dangerous.

In other accessible sections, the smell was overpowering and at times eye-watering.

The Creek Trail is a popular spot with families and dog walkers, and is well-maintained, grassy and green.

A large playground sits at the start of the trail, and on most days the spot is a lovely and peaceful walk.

Today the fuel sits on top of the water like used cooking oil – in some places a rainbow sheen, in others clearly formed globules.

Firefighers worked to block the creek off at one end, deploying floaters to soak up much of the petrol.

At the end closest to the road, fire fighters had opened up one of the drains that runs into the creek and were trying to pump foam off the top of the water.

"That stuff is probably more dangerous than the fuel", one firefighter said.

Meanwhile the tanker continued to slowly leak even as fire crews on the Calder began to decant its load.

The nearby Keilor campus of Penleigh Essendon Grammar School was part-evacuated during the incident, with fire crews asking school staff to pull students back from the part of the campus that borders the road.

About 1000 students attend this campus, and many of them enjoyed a day confined to the oval or watching movies in class. 

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