Bloom announcement: Late season cyanobacterial blooms co-dominated by Microcystis flos-aquae, Lyngbya birgei, and Aphanizomenon flos-aquae complex in Hamilton Harbour (Lake Ontario), an area of concern impacted by industrial effluent and residential wastewater.

Hamilton Harbour is a large embayment (approximately 22 km2, over 2.8 × 108 m3, maximum depth 23 m, mean depth 13 m) at the western part of Lake Ontario with a long history of anthropogenic impacts, particularly from industrial effluent and residential wastewater [1]. Designated an area of concern (AOC) under the Great Lakes Water Quality Agreement (GLWQA) in 1987, it continues to suffer from the buildup of hazardous chemicals in the water and sediments as well as eutrophication [3], [4], [5]. Several creeks (Spencer Creek, Redhill Creek, Grindstone Creek, Chedoke Creek) contribute to total water inflow (∼9.7 m3/sec) but a significant volume originates from two large wastewater treatment plants - the Woodward Avenue Wastewater Treatment Plant (∼40%) servicing the city of Hamilton and the Skyward Wastewater Treatment Plant servicing the city of Burlington (∼13%) [6]. The most significant water exchange between Hamilton Harbour and the rest of Lake Ontario is via a narrow channel on the east side of Hamilton Harbour, the Burlington Shipping Canal [1]. In 2017, cyanobacterial and harmful algal blooms (cHABs) were observed and characterized along Bayfront Park Beach in Hamilton Harbour, Ontario, Canada (Fig. 1, Fig. 2). The beneficial use of Bayfront Park Beach has been classified as impaired for beneficial use impairment (BUI) #8, Eutrophication or Undesirable Algae, and BUI #10, Beach Closings and Water Contact Sports, under the Hamilton Harbour's Remedial Action Plan. As part of Environment and Climate Change Canada's Great Lakes Action Plan, monthly sampling of whole water grabs, within and outside the blooms, occurred from July to November inclusive. In July and August a mixed community of chlorophytes and cyanophytes dominated the bloom, which exceeded 100 mg/L in phytoplankton total biomass (TB) (Fig. 3) [2]. By September, this already high TB increased dramatically beyond 3,000 mg/L before subsiding below 50 mg/L in October, a likely consequence of more turbulent waters in early autumn (Fig. 3). The community in September was dominated by Microcystis (60% TB M. flos-aquae and 16% TB M. aeruginosa) and Lyngbya (15% TB L. birgei). In November, TB exceeded 4,500 mg/L, with M. flos-aquae expanding its dominance (95% TB) while L. birgei was replaced by Aphanizomenon flos-aquae, albeit with reduced biomass (3% TB) (Fig. 3). It is suspected, based on spatiotemporal observations of bloom dynamics and circulation patterns within Hamilton Harbour, that phytoplankton biomass proliferates offshore and is transported by winds and currents to Bayfront Park Beach, where it is captured and accumulates within its crescent-shaped shoreline (Fig. 1, Fig. 2) [7]. Open in a separate window Fig. 1 Satellite imagery (aerial view) of Bayfront Park Beach, Hamilton Harbour, Lake Ontario (Ontario, Canada) where samples of the 2017 cyanobacterial and harmful algal blooms were collected. Note the crescent shape of Bayfront Park Beach and adjacent parkland, making it susceptible to localized accumulations of material.

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