Halifax Regional Municipality wants people and pets to stay out of two areas in Lake Banook due to suspected blue-green algae blooms.
One site is just west of the Paddlers Cove facility at 300 Prince Albert Road and the second is located further west along the same stretch of shoreline, closer to the intersection of Prince Albert Road and Sinclair Street.
"Blooms were identified there earlier this week … and may pose health risks to people and pets alike," said Cameron Deacoff, Halifax's environmental performance officer. "They should avoid the area until further notice.
"To the best of our knowledge, other areas of the lake are not affected. We do monitor our supervised beaches. We've contacted all the operators of the aquatic facilities around Lake Banook so that they're all aware of the risk and have sort of heightened awareness in general of algae blooms."
It's the second advisory the city has issued this summer.
A previous warning was issued earlier this month after blue-green algae blooms were discovered in a section of Lake Micmac near Shubie Park. It is an area popular with dog owners.
"We will be having testing done next week," Deacoff said.
However, it can take more than a week to obtain the results to confirm what toxins might be present.
A followup test will likely be necessary, Deacoff said. Until then, the three areas will remain closed to swimming.
Algae are present in freshwater and saline environments, however, these organisms can multiply rapidly during the summer, leading to extensive growth called a bloom.
The current heat wave is believed to have accelerated algae production earlier than usual in the season.
It is during the decay of some of the types of blooms that toxins can be released into the water, posing a risk to people and pets.
The toxins can cause skin, eye and throat irritation, and in serious cases where the toxins are consumed, can cause gastrointestinal illness. Children and people with compromised immune systems are at a higher risk for the more severe effects.
A blue-green algae bloom can appear as surface scum or discoloured water. They are not always easy to identify, Deacoff said.
"Blue-green algae blooms typically look like they have a colour that's blue-green but that is not the only colour form that they have," he said.
"They may also be green or red or brown or even yellow colour. They can appear as a surface scum, foam or matte. They really do have a wide variety of appearances. Some of them look like paint streaks and others are really hard to observe at all."
The blooms in the Dartmouth lakes "do have a classic blue-green appearance and it is a little bit below the surface of the water," he said.