The colloquial term for it is ‘gunk’. Dark green. Sticky. It clogs drains, it pools in the tanks of plastic water guns left out in the rain. It grows in drainage ditches, gutters, and puddles. It’s wet, it’s slimey, and to most people, it’s insignificant. But what is gunk? In this lab, I set out to characterize it.
I conducted this project as part of Professor Pringle’s EEB321 class at Princeton University.
In Florida, finding gunk is easy. At the bottom of a planter, in the valley used to collect runoff rainwater, I found a large sample.

The water was murky with dark green particles floating in suspension or large chunks adhered to the bottom and sides of the drainage valley (above). I took a sample of water from a particularly deep puddle in the valley (below), and analyzed it using the foldoscope under standard magnification.

A fast glance reveals that ‘gunk’ is anything but insignificant. Under a foldoscope, the sample is teeming with life. Green cells swirl and spin through the watery ether, dodging bubbles, and riding the micro-currents and nano-tides in a pin-prick of water. Families of cells hug together, their comraderie shaping giant superstructures, as they float through water, transforming sunlight into the nutrients necessary to add more citizens to their mobile micro-cities.

While gunk may seem to have a haphazard orientation at the macroscopic level, a look into its microstructure reveals highly associated, co-dependent structures. Here, we see a spherical association of algal cells.

Here, algal cells cling to the sides of a larger piece of plant debris.

Here, an amoeboid association of algae drifts above a gathering of bubbles.

My investigation revealed that ‘gunk’ is not just the curse of clean drains; it’s actually a highly associated mat of algal colonies. This discovery highlighted an interesting disjuncture between how we perceive the macroscopic world and the beauty that lies in the microcosmos. We may write ‘gunk’ off as unpleasant due to how it presents to the naked eye. But what lies beneath ‘the visible’ is a realm of countless fascinations.