Hamilton staff to try 'experimental treatments' to reduce harbour's stinky, toxic algae blooms

City staff are working on long-term plans to prevent toxic and smelly algae blooms at the Hamilton harbour – and short-term plans to mitigate blooms when they happen – but are cautioning residents that it's not the type of problem with a quick fix.

In a report that came before city council's public works committee on Monday, Hamilton Water staffers presented preliminary research into ways to help mitigate blue-green algae blooms.

The algae – called cyanobacteria – is toxic to humans and animals, and engulfed the area around Bayfront Park and Pier 4 in a putrid stench for several weeks this past summer while its massive blooms were rotting.

The report recommends testing out several "experimental treatments" to help prevent or remove the rotting mats of algae, said Cari Vanderperk, Hamilton Water's director of Watershed Management. 

Those include aerating and circulating the water to make it harder for the algae to flourish; introducing aquatic plants that absorb nutrients and limit sun exposure to the algae; and skimming the blooms off the surface.

Hamilton Water has added $500,000 to its 2025 budget to test out such solutions and evaluate their success. City staff are also working on a watershed action plan that would reduce urban and rural runoff, a main source of the nutrients that end up in the water and feed the algae. But that won't result in less algae for several years, Vanderperk said.

"That future could be five years away. It could be 10, it could be 20," she told councillors on Monday. As for the short term, "I don't think there's a municipality and country on the planet that has been able to throw enough money at this problem and have it solved," she said.

The report noted that the city has installed mechanical mixers and aeration devices in the harbour in the past, only to see them "regularly impacted by vandalism or theft." It also tried "nominal surface vacuuming" of the algae, but later learned that specific cyanobacteria species reproduce by fragmentation, so vacuuming made things worse.

"Disturbances of some species can accelerate growth, resulting in more toxins in the water and causing more odour compounds to be released. There is an additional risk that the cyanobacteria toxins become airborne when blooms are disturbed potentially causing health and safety issues in the area," says the report.

Nick Winters, director of Hamilton Water, previously said the algae thrived this year in particular after wet weather washed nutrients from throughout the watershed, such as fertilizers, into the bay. Combined with the hot, sunny weather, it gave the toxic algae just what it needed to thrive and reproduce, he said. 

Coun. Maureen Wilson (Ward 1) said at a meeting in August the situation should serve as a "red flag" about the combined efforts of climate change and development policy, a sentiment she repeated again this week.