If the surface layer is organic, it breaks apart and stays apart in broken, angular pieces. Later in the summer, there's another natural phenomenon that often sparks calls to the Spill Line. If conditions are right, a form of algae that grows in Yukon waters multiplies rapidly and forms sheets that look remarkably like toilet paper. The sheets catch on branches or get tangled in fishing nets, prompting calls to the Spill Line about a possible sewage leak. Under a microscope, the resemblance to soggy toilet paper disappears, says Arrell.
Magnification reveals the cellular structure of the algae.
Although the algae bloom occurs naturally, the staff at Environment Canada don't mind when people report it. There are several other common natural phenomena that people often mistake for chemical or fuel contamination, Arrell says. In June, when pine trees release their pollen, the pollen settles like dust on the surface of ponds and lakes. Often, the wind blows it across the surface and concentrates it in small bays, where it forms greenish-yellow scum that looks unnatural to some people. Occasionally, a red scum appears.