Nova Scotia

Ecosystem revival set back by unexpected algae bloom in Dartmouth lake

Efforts to restore the ecosystem around Dartmouth's Oathill Lake have likely been undone by an unexplained bloom of algae, a local conservation group says.

Conservation group has noticed irregular amount of green algae collecting on surface of Oathill Lake

Oathill Lake is the only lake in the area with a sewage pumping station. (Nic Meloney/CBC)

Efforts to restore the ecosystem around Dartmouth's Oathill Lake have likely been undone by an unexplained bloom of algae, a local conservation group says. 

Members of the Oathill Lake Conservation Society (OLCS) noticed an irregular amount of green algae collecting on the water's surface over the weekend. Algae blooms are uncommon at this time of year, raising questions about the cause.

Families who've lived on the lake for nearly 50 years say it's never bloomed to this extent, the group says.

Years of effort to restore the lake's ecosystem may be undone by the sudden bloom, the Oathill Lake Conservation Society says. (Submitted by Bob Rutherford)

The OLSC has been working to restore the ecosystem for two years, installing a solar-power device that helps to circulate the water and scouring the shore for invasive species. 

Bob Rutherford, a habitat restoration biologist with the society, says while they've yet to determine the source of the bloom, algae's growth is driven by phosphorus.

That means it could be coming from a number of sources: plant fertilizer, animal or human waste, or water run-off from surrounding communities. But, he says, there are no obvious explanations.

"We haven't seen anything different in this watershed this week," says Rutherford, noting that the nearby Penhorn and Maynard Lakes are currently normal.  

"The only thing unique about this lake [compared to] the other two, is the sewage pumping station at [one end]. The bloom does appear to start at that end of the lake." 

Local families say algae blooms haven't been this rampant in nearly 50 years. (Submitted by Bob Rutherford)

Halifax Water operates a pumping station at the south end of the lake, which Rutherford says has overflowed into the lake in the past — but only after heavy rainfall or snow melt. 

Halifax Water told CBC News that nothing out of the ordinary has been reported at that station over the last week. 

The OLCS has taken samples to be processed by their biologists and are also hoping to have testing done for coliform bacteria levels, which can be harmful to humans. The costs of lab tests will be an out-of-pocket expense for the non-profit society, Rutherford says, adding they're essential to determine whether the water is safe.

Children swimming in the lake as recent as Sunday, Rutherford says, and even if the results reveal the water is safe for humans, wildlife will likely suffer side-effects.

The society has been working to regulate oxygen levels in the water after years of harmful pesticide and waste dumping, and Rutherford says the sudden growth and decay of the algae will essentially undo years of progress.


Nic Meloney


Nic Meloney is a mixed heritage Wolastoqi video journalist raised on Cape Breton Island in Nova Scotia/Mi'kma'ki. Email him at or follow him on Twitter @nicmeloney.