Eek! What is that Sheen on My Water?

Spring is a time of change. Spring brings changes in our waters as well. Some of these changes are visible on top of the water and cause concern among water users and viewers. Let’s dispel some of these concerns associated with the spring season.

Sometimes, water users and viewers notice what appears to be oil floating on top of the water. Could this be oil? Potentially. Could this not be oil? Most likely. Plants perish, and decomposition occurs, typically during the spring and fall seasons of the year. Much of the decomposition that happens in spring is associated with the initial growth and development of plants. Bacteria living in the soils within and around the water break down the perished plants. These bacteria are decomposing the old plant material. The waste product produced from the bacteria’s decomposition of the old plant material is an oily substance. The oily sheen on the water is a waste product of bacteria. Frequently, the oil accumulates in portions of water where there is little to no water movement. As the decomposition process completes, the oily sheen should lessen over the next few days to weeks. This bacteria-produced oil from decomposition is a natural process.

Petroleum-based oil seen on water is not a natural process. Petroleum-based oil could enter water from various sources, such as but not limited to transportation spills, stormwater runoff, and improper disposal of products containing oil. Like the oily substances produced by bacteria during decomposition, petroleum-based oils will float on top of the water and accumulate where there is little to no water movement.

Here are some tips to identify the difference between oils in water:

	Bacteria-produced Oil	Petroleum-based Oil
Appearance	Oily sheen on top of water with little to no difference in color throughout	Oily sheen on top of water with differences in color throughout (may even appear like a rainbow)
Touch (use a stick)	When disturbed, the sheen breaks away easily with irregular patterns and does not reform. The oil will not adhere to the stick.	When disturbed, the sheen swirls, elongates, and does reform. The oil may adhere to the stick.
Odor (not always present)	Strong organic, musty, or earthy smell.	Volatile organic compounds (VOCs) smelling like gasoline or diesel fuel.

Another sheen on our waters that is frequent during Florida’s springtime is pollen. Pine, tree, and weed pollen accumulate on top of water, especially in areas with little or no water movement. If the sheen on the water is yellow, orange, or sometimes white, this is most likely due to pollen. Think about how pollen shows on a car in Florida during spring…our waters can show the same to some extent.

Let’s give it a try! See if you can identify the sheens in water in each photo—answers at the bottom of the page.

Photo 1

Photo 2

Photo 3

Photo 4

Photo 5

Photo 6

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PHOTO ANSWERS: Photo 1: Bacteria-produced oil sheen. Photo 2: Pollen sheen. Photo 3: Petroleum-based oil sheen. Photo 4: Pollen sheen. Photo 5: Petroleum-based oil sheen. Photo 6: Mixture of bacteria-produced oil and pollen sheen. Note all photos were obtained from Adobe Stock Photos.