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Algae in Storm Water Detention Ponds

Periodically, The City of Red Deer experiences algae blooms in some of its storm water detention ponds. The following information will help you to understand why this occurs and what you can do to help minimize this problem.

What is algae?
Algae are aquatic plant-like organisms that can conduct photosynthesis, but lack true stems, roots and leaves. Algae are naturally present in most freshwater bodies and form the basis of the aquatic food chain. There are many different species of algae, ranging from tiny, almost microscopic organisms to larger more complex structures, such as seaweed. Since most forms of algae require sunlight to grow, they usually occur on the surface or within the first 3 to 6 feet of water. It is estimated that up to 80% of the food and oxygen production on earth is from algae growth in freshwater and ocean ecosystems.

What is an algal bloom?
When conditions are favorable for rapid algae growth, they reproduce explosively and accumulate in dense concentrations. This is called an “algal bloom”. An algal bloom may turn the water green or appear as scum, foam or a grease-like sheen on the surface of the water. Algal blooms may also appear as floating mats of “stringy hair” or may look like thick patches of submerged vegetation.

What causes algal blooms?
Algal blooms occur naturally in slow moving water and are often triggered by warm, sunny weather. The likelihood of a bloom depends on conditions within the specific water body. Although algal blooms are a natural phenomenon, nutrients such as dissolved nitrogen and phosphorous will intensify algae growth. These nutrients may come from rotting vegetation on the bottom of the pond or will be carried into the pond in storm water runoff that contains fertilizers or animal waste. An absence of algae-eating organisms and a lack of competition for nutrients will also exacerbate the problem.

Are algal blooms dangerous?
The City of Red Deer has never had to address a dangerous algal bloom. Most algae species are harmless, and do not pose a health hazard to residents, however, there are some organisms, such as blue-green algae, that can produce a toxin that is dangerous to fish, animals and people. Although blue-green algae is actually a type of bacteria (called “cyanobacteria”), it is often confused with algae because it appears as a thick scum that resembles paint floating on the surface of the water. The toxins from blue-green algae are released into the water once the bacteria die. If a toxic algal bloom were to occur in Red Deer, The City would notify residents and take immediate steps to reduce the risk of potential exposure.

Although swimming is not allowed in any of Red Deer’s storm water detention ponds, you should never swim or wade in or allow your pets to swim in or drink any water containing visible algal blooms. Some types of algae can cause skin irritation and consuming water containing toxins can cause illness and possibly even death. Fortunately, most blooms are short-lived and an affected area will likely be safe again within one or two weeks.

How does The City address algal blooms?
A certain amount of algae is a natural and important part of a healthy aquatic ecosystem. Although it is important to keep algal growth in check so blooms do not occur, The City must deal with each situation individually, since every pond has a unique set of conditions.

The most effective way to deal with algal blooms is to prevent them by reducing the amount of nutrients in the water. Removing decaying vegetation from the pond will reduce nutrient input, while allowing emergent vegetation, such as cattails, to grow in and around the pond helps to absorb nutrients from the water. These plants also deter geese from colonizing the area, reducing the amount of animal waste that may be washed into the water. Altering conditions within the pond by decreasing sunlight penetration or increasing water and oxygen flow also decreases the likelihood of an algal bloom.

There are several chemical and non-chemical options available to treat algal blooms once they have occurred. If treatment is necessary, The City will determine the most appropriate action to address each specific situation. Activities that affect surface water and/or fish habitat are regulated by Alberta Environment and Fisheries and Oceans Canada. Since the water from storm water detention ponds eventually flows into the Red Deer River, regulatory approval will be required before any chemicals can be applied.

What can I do to prevent algal blooms?
The most effective way to deal with algal blooms is to prevent them from happening in the first place. Reducing the use of lawn fertilizers and cleaning up after pets will prevent additional nutrients from washing into ponds with storm water run off. All storm water in Red Deer eventually flows into the Red Deer River and is not treated at the Waste Water Treatment Plant. Preventing chemicals and nutrients from contaminating storm water will not only help to prevent algal blooms, but will also help to protect our drinking water supply.

Where can I find more information?
For more information on The City’s algae control practices, or to report an algal bloom, call 342-8750.