One of the sediment samples had trace amounts of polycyclic aromatic hydrocarbons, while the other two — gathered from the Ells and Steepbank rivers — had significantly higher levels of bitumen, ranging from 4.66 to 6.48 parts per million.

Researchers put fish eggs in the sediment samples then let the fish hatch and live in the water for three weeks.

Fish hatched in two bitumen-rich samples were about 25 per cent shorter in length and 30 per cent lighter than those born in the cleaner water. They also developed deformities that included jaws that don't close properly and short tails.