How you can stop your lake from turning blue-green

• Scrap the lawn in favour of natural groundcover. Don't use fertilizers or pesticides.
• Help keep nutrients out of the water by maintaining natural vegetation along the shoreline (on land and in the water) and keeping your property well forested.
• Use phosphate-free detergents and cleaners. (Be especially vigilant if you run an automatic dishwasher, since most of those detergents are high in phosphorus. Use phosphate-free products like EcoEthic or Nature Clean.) Never use any soap or shampoo in the lake itself.
• Maintain the septic system and have it pumped regularly. Avoid bleaches and anti-bacterial soaps, which disrupt septic-system function.
• Minimize boat wake. Try not to churn up lake sediment.
• Reduce hard surfaces around the cottage to cut storm-water runoff. Opt for more permeable stone and gravel instead of concrete and asphalt. Choose meandering routes for paths or lanes. Incorporate swales and “rain gardens” (depressions with moisture-loving plants) to slow rainwater and help it infiltrate the soil.
• Support your cottage association and/or lake stewardship group.

What is that stuff?

In its early stages, only a specialist with a microscope can sort out what's what, so when an algal bloom turns the water green and cloudy the safest approach is to stay out of the lake (and keep your pets away, too). Here are some tips to help you tell what is – and what isn't – cyanobacterial.

A cyanobacterial bloom is:

• Most notable for the way it covers the water with a fluorescent blue-green paint-like scum.
• Often redolent of fresh grass clippings, must, mould, or decaying vegetation.
• Usually blue-green (almost a bright emerald or teal, not kelly or forest green) but may have brown or reddish tinges.
• Often likened to pea soup.
• Most likely to occur in mid-to-late summer (July, August, and September).
• Made up of small colonies (the size of a pinhead or smaller) that are hard to pick up and hold on a stick.

A cyanobacterial bloom is not:

• A subsurface cloud that's bright green (this is likely green algae) or brown (likely chrysophytes or diatoms, both other types of algae).
• Yellow, powdery stuff floating on the lake. (This is tree pollen.)
• Anything with root-like or leaf-like structures. (Duckweed is a small floating plant sometimes mistaken for blue-green algae.)
• Guilty of releasing a sickly sweet odour. (Blame chrysophytes for that.)
• Long and stringy when you pick it up with a stick. (These are usually colonies of green filamentous algae.)

Finally, when you see algae in the lake, it's best to err on the side of caution. Even if the bloom doesn't look blue-green, that doesn't mean there aren't blue-greens around.

Related Articles

Blue-Green Algae on Three Mile Lake

Blue-Green Algae on Other Lakes

Published in the April/May 2006 issue of Cottage Life.

Copyright © 2006 by Cottage Life. All rights reserved. Reproduction of any article, photograph, or artwork, for other than personal use, in whole or in part, without the written permission of the publisher is strictly forbidden.