Thousands of fish are congregating in Lake Huron’s warm waters near an Ontario nuclear plant, creating a spectacular sight now captured in exceptional detail. Documentary filmmakers Yvonne Drebert and Zack Melnick are utilizing a cutting-edge $250,000 underwater drone, one of a rare few globally and the sole one in freshwater operation, to film parts of the Great Lakes that are typically inaccessible due to depth or remoteness.
CBC News has been granted exclusive access to footage from one such dive ahead of an upcoming livestream event scheduled for Earth Day to promote their new documentary Hidden Below: the Great Lakes, showcasing unique wildlife from the Earth’s largest freshwater ecosystem.
The drone is focusing on the warm water discharge from the Bruce Nuclear Generating Station, close to Tiverton, Ont., where fish congregate for shelter and food. The station, the largest nuclear plant in North America, releases water for reactor cooling, creating an area with elevated temperatures that attracts a variety of fish.
‘Fish city’
The extraordinary imagery captured by Melnick and Drebert in cinematic 4K showcases scenes akin to the ocean, with countless silver gizzard shad shimmering in the sunlight, accompanied by other species such as bigmouth buffalo, walleye, bowfin, salmon, trout, catfish, and carp. “No one had the opportunity to explore beneath the water there before, and it was truly breathtaking,” remarked Drebert.
Melnick referred to the site as “fish city,” highlighting the unusually dense concentration of fish in the area.
Scientists explain that the warmer water in the plume fosters a rich food source for the fish, enhancing nutrient circulation and promoting algae growth. The vegetation attracts fish that feed on it, which in turn attract predators.
The illusion of abundance
“Most of the Great Lakes feature these thermal plumes,” noted Nicholas Mandrak, a leading freshwater fish scientist from the University of Toronto, who will provide live commentary during the Earth Day stream of the “fish city.” These significant thermal plumes stem from power plant cooling systems, industrial discharges, wastewater treatment outflows, and river mouths.
While the sight of millions of fish gathering in warm waters may suggest abundance, scientists caution that it could signify a fundamental shift in the ecosystem. Mandrak explained that the fish concentrate around thermal plumes due to depleted food sources in the main lake, indicating an ecosystem altered by invasive species.
Mandark’s reference to “mussels” pertains to zebra and quagga mussels, invasive species from Europe that have proliferated in the Great Lakes since the 1980s, causing ecological and economic harm. These tiny shellfish filter plankton from the water, diminishing food availability and reshaping the habitat.
Bruce Power stated that the warm water plume’s size varies based on lake conditions, with regulated discharge temperatures allowing for a temperature increase of up to 11 C in summer and 13 C in winter.
Sapna Sharma, an environmental stressor researcher from York University, highlighted the impact of warmer waters on native fish species, potentially enabling invasive species to thrive in northern ecosystems. She emphasized the importance of safeguarding the Great Lakes, which support various sectors and millions of people.
A 2020 report for the Saugeen Ojibway Nation mentioned warm spring conditions as a factor in Lake Huron whitefish declines, attributing it to multiple stressors like invasive species and habitat changes.
Sharma reiterated the significance of the Great Lakes and the need to investigate unusual occurrences like the “fish city” to understand potential ecosystem changes and their implications for dependent communities.