Cottage Q&A

QUESTION
Last August, when it had been hot for some time, we found a couple of huge algae growths close to the shore in Virtue Lake, near Parry Sound. They were about two metres long and blown up like a balloon with a thin, green, slippery (not slimy) skin. They did not reappear. Should we be concerned about the health of the lake? By October, there were quite a few frogs around, which we heard indicates good water quality. Or is this a myth?

Irmgard Titze, via e-mail


ANSWER
We took your question to Bev Clark, coordinator of the Ontario Ministry of the Environment's Lake Partner Program at the Dorset Environmental Science Centre. He is wary of identifying an organism without his microscope, but says it's probably filamentous algae. It's often called blanket weed, elephant snot, or pond scum, but by any name it doesn't seem you have much to worry about. When it's thriving, filamentous algae appears as a large green blob of slender threadlike bodies near the bottom of a lake. In late summer and fall, clumps die and float to the surface en masse. These decaying mats can trap gases produced by decomposition and puff up. The small number you spotted does not suggest to Clark unusual levels of algae, nor any changes in water quality; rather, he believes last summer's high temperatures are the likely cause of your sighting. Hot summer or not, rest assured that filamentous algae can grow in areas with excellent water quality. (Blue-green algae, on the other hand, can produce toxins. For more on this, read "What Happened Last Summer at Three Mile Lake?")

When it comes to assessing water quality, however, frogs may be even better than lake scientists. Andrew Lentini, curatorial keeper for amphibians and reptiles at the Toronto Zoo, says frogs and other amphibians such as toads, newts, and salamanders are a pretty reliable indicator of the health of your lake. Frogs constantly absorb water through their skin and are particularly sensitive to harmful agents that cause poor water quality. A declining population may indicate problems

Steve Brearton



* Published in the July/August 2006 issue of Cottage Life