Last weekend, three dogs died almost immediately after playing in the Saint John River near Fredericton.

Though officials are still trying to determine if blue-green algal toxicity killed the animals, people are being warned to keep kids and pets away from any water with green scum on the surface.

Given the warning, many people are asking: What is blue-green algae and how dangerous is it?

Here's five things you need to know:

1. Algae blooms are most common in summer or early fall.

That's true, but according to the National Collaborating Centre for Environmental Health, blue-green algae -- also known as cyanobacteria -- can occur in Canada at any time of year. The microscopic organisms can be found in fresh, brackish or salt water.

Janice Lawrence, an associate professor of biology at the University of New Brunswick in Fredericton, studies toxic algo blooms. Lawrence says cyanobacteria are actually different from algae.

"Cyanobacteria are a group of bacterias that are capable of photosynthesizing, so they can harvest the sun's energy for their basic function -- so they're separate," Lawrence says.

"The reason we call them cyanobacteria is because they have a cyan or blue-green colour, and that comes from the pigments they use to harvest the light."

Cyanobacteria are often confused with regular algae, which is green and lives in the same environments.

2. Not all cyanobacteria are toxic.

However, every bloom should be treated as if it is toxic.

"They become troublesome when they produce toxins, and only a very small proportion of cyanobacteria produce toxins," Lawrence says.

Between 80 to 100 different compounds have been discovered in these blooms, and all have different levels of toxicity.

They're generally grouped into three classes: those that affect skin; those that affect the liver; and those that affect the nervous system.

3. The toxins have similar effects on humans and animals.

Cyanobacteria can produce cyanotoxins, which in high concentrations are harmful to animal and human health. In rare cases, exposure has been fatal to humans.

The toxins that affect the nervous system can affect breathing.

"Your diaphragm no longer works so you can't breath," says Lawrence. "You suffocate."

4. People should take these public health warnings seriously.

Lawrence says she went rowing on the Saint John River on Friday morning, but she took precautions.

Splashing around in the water can create aerosols, which can be ingested or inhaled.

"I waded in with my boat and I made sure I washed everything really well when I got home," she says.

"I was just very careful not to ingest anything and not splash around very much. And I didn't take my dog to the river, nor my young son -- and I won't until I know what the source of the toxins is."

5. Blue-green algae grow in warm conditions when water levels are low and can produce toxins that can affect the brain.

Provincial veterinarian Dr. Jim Goltz has said the dogs in question died within a half-hour of being in the river.

That fact is a key concern for Lawrence.

"If it is a neurotoxin, it had to be fairly concentrated because of how rapidly they died," she says. "And the locations were on opposite sides of the river -- Carleton Park and Hartt Island, about seven kilometres apart. So that's quite a distance."