Is That Oil in the Water?

image of oily bacteria

All storm water that falls on campus eventually makes its way to the Arboretum Waterway – the lowest place on campus and the largest component of the campus’s stormwater infrastructure.

To ensure that most of the water that reaches the Waterway is clean of contaminants, Arboretum and Public Garden staff work closely with many different university departments including Campus Planning and Environmental Stewardship and Environmental Health and Safety to incorporate landscape elements like rain gardens and bioswales into our landscapes, especially along roads and around parking lots.

These landscapes help filter contaminated water from parking lots before it reaches the Arboretum Waterway, which is why, despite the number of roads and parking lots on our campus, we rarely see oil in the Waterway. But, we do see something similar…

Naturally occurring, iron-oxidizing bacteria can create a film similar to oil (see photos), however it is completely harmless and goes away over time.

bacteria film breaking up on water surface

How can you tell the difference between oil and bacteria in the Arboretum Waterway? If you observe the film break up when it comes into contact with something like a branch, then it is bacteria! Oily surfaces will come back together immediately after being disturbed.


If you believe that film seen on the Arboretum Waterway is oil, please contact
UC Davis Environmental Health and Safety.

Phone: (530)752-1493
Email: enviroteam@ucdavis.edu

This content was developed with help from students on our Learning by Leading Museum Education team.

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