Effects of Changing Lake Temperatures on Developing Fish Embryos in Lake Huron

Many industries use lake water to cool their plants and water that returns to the lake can be warmer than the typical lake temperature. In Ontario, Bruce Power’s nuclear generation station uses water from Lake Huron for cooling; the water that is discharged back into the lake can reach up to 38°C. This causes water temperatures to fluctuate, with areas near the discharge being much warmer than others. This study explores the effects of varying water temperature on the development of lake whitefish embryos near the plant.

McMaster Researcher


Wilson J.Y., Thome C., Mitz C., Somers C.M., Manzon R.G., & Boreham D.R., " Incubation of lake whitefish (Coregonus clupeaformis) embryos in cooling water discharge and the impacts of fluctuating thermal regimes on development," Canadian Journal of Fisheries and Aquatic Sciences, 73, (2016) 

Funded by


Bruce Power

What is this research about?

Lake whitefish are a cold-water species that spawn in late fall when lake temperatures drop below 10°C. Embryos develop over the winter and hatch in the spring. This species is found in Lake Huron. The Bruce Power nuclear generation station is located on the eastern shore; the station takes lake water for cooling and then discharges it back into the lake. This process causes  areas of the lake near the power station to experience varying temperatures. The purpose of this study is to explore the effects of these changing lake temperatures on the development of lake whitefish embryos. The researchers predicted that fluctuating lake temperatures which remain within the species' optimal development range (0.5°C to 6°C) may speed up embryonic development. 

What did the researchers do?

In December of each year, from 2011 to 2013, researchers placed five to seven custom-built incubation chambers at four sites along Lake Huron’s eastern shore.  Each chamber held 100 embryos. Two study sites, located offshore from the generating station, where water temperatures are affected were selected to allow researchers to study the impact of the water temperatures (impacted sites). Another two sites where water temperatures were unaffected by the power station were used for comparison (reference sites). Researchers attached data loggers to the chambers to record lake temperatures at 5 minute intervals. Each spring the chambers were retrieved. The researchers were able to calculate: 

  • Daily average and daily maximum temperature at each site for each year 
  • Daily range and rate of temperature change at each site for each year 
  • Length of time it took to each embryo to hatch (for chambers retrieved after hatching occurred) or how far development had progressed (for chambers retrieved before hatching occurred) 
  • Total body length, eye diameter, and yolk area of embryos or fish. 

What did the researchers find?

Due to various factors, not all chambers, data loggers, and embryos could be retrieved. From the ones that were retrieved, the researchers found the following results: 

  • In all three years, the impacted sites had warmer temperatures on average than the first reference site. 
  • In all three years, the impacted sites experienced more daily temperature fluctuations than the first reference site. 
  • In the second year, embryos retrieved from the impacted sites had significantly larger body lengths compared with embryos retrieved from the first reference site. 
  • In the third year, the chambers retrieved from one of the impacted sites contained hatched fish that were larger than embryos retrieved in the second year. 
  • In all three years, time-to-hatch for embryos from impacted sites was shorter than time-to-hatch for embryos from the reference sites. 
  • In the second year, embryos from impacted sites were approximately 10% closer to hatch than embryos from reference sites. 

Overall, the data showed that impacted sites experienced warmer and fluctuating lake temperatures, which sped up lake whitefish embryo development without increasing mortality or developmental abnormality levels.  

How can you use this research?

This research is useful to those concerned with the protection of fish and other aquatic species. It demonstrates that industrial cooling processes can have an impact on the development of fish and other animals. In this case, the impacted sites resulted in advanced development. However, the research suggests that industrial cooling processes have the potential to increase lake temperatures to levels that may cause increased mortality or abnormalities. This research may also be useful to biologists and policy makers, as it provides a foundation to begin exploring how warmer, fluctuating lake temperatures can affect the growth and survival of freshwater fish.    

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