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How Algae Blooms Work

Posted on August 25, 2017

Algae bloom at FortWhyte Alive, July 2014

How Algae Blooms Work

Algae blooms are a common sight in many lakes in Manitoba.These spreading waves of green can wash up on beaches or float around in the water. Algae begin growing during the springtime, and continue throughout the summer, preferring standing water with a temperature of 25°C or higher.

Cyanobacteria, also known as blue-green algae, are the most common type of problem algae in Lake Winnipeg. In addition to building their own sugars through photosynthesis like other plants, blue-green algae can also produce their own fertilizer by capturing nitrogen gases from the atmosphere. In lakes with high amounts of phosphorus, blue-green algae are able to outcompete other kinds of algae.

Where does this phosphorus come from? The Lake Winnipeg Watershed includes four Canadian provinces and four U.S states, an area of about 1 million square kilometres. The phosphorus that fuels algal blooms arrives in  Manitoba through rivers and streams. Sources include urban wastewater, agricultural fertilizers, livestock manure, and natural sources. Overland flow during spring melt leaches phosphorus from dead plant matter and delivers it in one big burst into the lake ecosystem.

People often confuse cyanobacteria with green algae because they both produce thick layers on the surface of the water, have unpleasant odors and reduce the levels of dissolved oxygen in the water, which can lead to fish kills. Both types of blooms can have a negative impact on the lake’s health. However, green algae do not produce nerve or liver toxins, while cyanobacterial blooms can. It is unpredictable how high the concentration of these toxins are within the bloom, but drinking contaminated water has been known to cause the death of animals, and swimming in it can make humans very ill.

Though we cannot necessarily control what is flowing in from outside our province, we can do our part to protect water close to home. Organizations such as the Lake Winnipeg Foundation, Manitoba’s Conservation Districts, and Ducks Unlimited are involved in education and research that helps to protect the lake. Local, provincial and national governments can be called upon to support projects that help keep our waters healthy, such as ending wetland destruction, supporting upgrades to wastewater treatment plants and more. We can each do our part by conserving water, preventing pollution, and stopping aquatic invasive species.

Want to learn more about how you can protect water? Get involved with citizen science through the Lake Winnipeg Foundation,check out a FortWhyte Alive workshop on stabilizing shorelines with willow plantings, or read up on water sustainability tips to assist you in reducing your water footprint.

Written by Émilie Ferguson, Summer Interpreter


Lake Winnipeg algal bloom illustrations drawn by Shawn Stankewich from algal bloom maps derived from satellite data by Greg McCullough; provided courtesy of the Lake Winnipeg Foundation.