Government of New Brunswick

Warm water temperatures, high amounts of light, wind and water currents, and high nutrient levels in lakes can all create the right environmental conditions for excessive growth of blue-green algae.  When blue-green algae grow in large quantities they create algae blooms which can cause clear water to become cloudy and result in the formation of scums when the algae float on the surface.  In New Brunswick, significant algae blooms in a few lakes have been present in the last few years.


When are algae blooms usually observed?

Although it is difficult to predict when an algae bloom will occur, in New Brunswick blooms are common during the hot, calm summer weather from early July to late September.  Algae blooms can dissipate quickly through wave action or can last for several weeks.

Algae blooms can reappear year after year as the algae that causes the blooms over-winters in a dormant stage in the lake.  If the cause of the bloom is not resolved, then the conditions may occur the following year causing algae blooms to re-occur.


What are the characteristics of algae blooms?

You may or may not see an algae bloom floating on the surface of a lake.  This is because algae blooms can be suspended at various depths in the water. They can also adjust their buoyancy as conditions require, moving where there are more nutrients and light.

Algae blooms can take on a variety of appearances, they can look like foam, scum, mats, or they can appear in colonies that resemble small balls or clumps.  On windy days algae blooms may accumulate near the shore.  For examples of algae blooms, please visit the cyanobacteria section of the NB Department of Environment’s abbreviated identification guide to New Brunswick's aquatic curiosities.


What causes algae blooms?

Blue-green algae can multiply quickly in a lake when the nutrient levels, in particular phosphorus and nitrogen, are high.  With the presence of abundant nutrients providing an abundance of food for the algae, a lake can very rapidly develop an algae bloom.  Other factors such as warm water temperature, slow moving water and shallow water, can compound the effects of a bloom allowing the algae to thrive.

Although nutrients are naturally occurring in a lake and are needed for plant and animal life, too much phosphorus and nitrogen can cause problems by offsetting the natural balance of the lake.  These problems arise or are compounded when storm water, agricultural runoff, industrial and wastewater effluent, faulty septic systems and lawn fertilizers find their way into the lake.


What are the effects of algae blooms?

Even seemingly benign algae blooms can impair the visual enjoyment of a lake, cause unpleasant odors, and may interfere with the safe use of the lake for diving and swimming by obscuring potential dangers that may lie beneath the water’s surface. Blooms may also foul water supply intakes or render the water not suitable for uses by cottagers, industry, municipalities or others.

Under certain conditions some algae may produce toxins that, with direct contact, can cause skin and eye irritation.  Although people do not usually drink water contaminated with blue-green algae because of the scum and accompanying smell (fresh blooms smell like newly mown grass and older blooms smell like rotting garbage), you can accidentally swallow contaminated water while swimming, water skiing or taking part in other recreational activities.  If this occurs, you may experience headaches, fever, sore throat, dizziness, stomach cramps, nausea, diarrhea and vomiting.  For more information on potential health effects of algae blooms, please visit the NB Department of Health’s Q&A’s.  . 

Excessive levels of the toxin can also be extremely harmful to fish and wildlife.  As algae die, they decompose using up the dissolved oxygen in the lake.  This reduces the amount of dissolved oxygen available to fish and other aquatic life.