Algal Blooms

Algae - Lac La Nonne What are Algal Blooms? - Every year during the warm summer months many Alberta lakes undergo visible but usually short-lived changes. Their clear, transparent water may suddenly take on a soupy appearance, often blue-green, bright blue, grey or tan in colour. The organisms responsible for these changes are microscopic plants called algae. When algae grow so thick that they make lake water look like pea soup, the condition is called an algal 'bloom'.

Blue-green algae are among the most common types of bloom-producing algae. Blue-greens are unusual algae because they share some typical features of both algae and bacteria. In some species the algae are tiny cells that cannot be seen with the naked eye, but in most species found in Alberta lakes, the cells are grouped in colonies. Under the microscope the colonies look like strings, flakes or globules and can reach a size of several millimetres. Colonies look like fine grass clippings, small shapeless clumps, or a homogenous soupy mass.

More than 100 species of blue-green algae have been recorded in Alberta. A typical summer lake water sample usually contains 20 or more blue-green species of algae. However, the most troublesome blooms in central Alberta lakes are caused by three species of blue-green algae: Aphanizomenon flos-aquae, Microcystis aeruginosa, and Anabaena flos-aquae.

These blooms become particularly visible during calm, hot weather. The algal cells contain small gas bubbles which cause them to rise to the surface of the lake and accumulate in scums. Wind and wave action concentrate these scums into bays, or along the shore where they begin to decompose. As the algae break down, pigments in the cells are released, often causing the water to turn a vivid purple, red or blue color. A coating, which looks like bright paint, may form on the sand and rocks along the shore. Strong, rotting odours are also produced when the algae die off and decompose.

When and Where Do Blooms Occur? - Blooms are most common in central Alberta lakes from late June to mid-September. In most lakes, blue-green blooms last for two or three weeks. In some lakes where different blue-green species develop one after another, blooms can persist throughout the summer and early fall.

Blue-green blooms are known to occur in relatively undeveloped lakes, and in those lakes with extensive watershed or shoreline development. In general, the more fertile - or nutrient rich - the lake, the more likely it is to display blue-green algae blooms.

Are Blooms Predictable? Blooms usually develop in nutrient-rich lakes in the summer when the water is warm and slightly to moderately alkaline. However, variations in air and water temperatures, total sunlight, and wind velocity also influence bloom development. Because these factors vary from year to year, blooms cannot be accurately predicted. Blooms may not occur every year in a given lake, or they may not develop at the same time each year. Also, the variety of species involved in a bloom may differ.

Why are Blooms Undesirable? - Floating scums or shoreline accumulations of blue-green algal masses are not aesthetically appealing, and people often complain about the appearance and colour of the water during the summer months. If blooms occur in reservoirs used as a municipal water supply, the water may have an unpleasant odour.

The decomposition of algae uses oxygen dissolved in the water. Occasionally, decomposing algae may deplete the oxygen to the extent that fish suffocate and die.

The threat of toxicity or poisoning is also associated with blue-green blooms. Intense and widespread toxicity has not occurred in Alberta lakes, although some cases have been severe enough to cause the deaths of domestic animals, waterfowl and other wildlife.

Recreational lake users should take special care during blooms and should treat any intense bloom with caution. Humans should not drink water from bloom-infested lakes and reservoirs, nor should they swim or wade in water containing concentrated algal material. Children should be supervised very closely. People should also take care to provide alternative water sources for domestic animals and pets.

What Can We Do About Algal Blooms? - Chemicals can be used to kill blue-green algae. Unfortunately, many of these chemicals are toxic to other forms of life, including fish and fish food organisms, and their use could create more problems than they solve.

A long-term solution is to reduce the amount of nutrients entering lakes. The main nutrient sources that can be controlled are sewage effluents, agricultural runoff, and industrial effluents. Cottage owners and recreational users of lakes can help reduce the nutrient inputs into lakes through awareness and individual action.

If you have a concern about a lake, contact the nearest Alberta Environment office in your region.

Alberta Research Council project targets blue-green algae (ARC news release)

For more information on this issue read about Blue-Green Algal Toxicity

Environment Home | Search | Contact Us | Privacy Statement | Minister's Office Expenses

Emergency Numbers

The user agrees to the terms and conditions set out in the Copyright and Disclaimer statement.

� 2009 Government of Alberta