SAINTE-MARIE — Water from the Chaudière River, which runs from the town of Lac-Mégantic to Lévis, where it flows into the St. Lawrence, remains safe to drink, an expert panel has concluded.



But the remains of the estimated 100,000 litres of crude oil that spilled into the river after July 6, 2013, when a runaway tanker train crashed and exploded in the centre of Lac-Mégantic, killing 47, remains a concern.



At different points on the river bottom, sediment remains contaminated, endangering the tiny aquatic organisms that fish, birds and amphibians feed on, and possibly jeopardizing fish reproduction.



David Heurtel, environment minister in the Liberal government of Philippe Couillard, said Monday that 100,000 litres "is a lot of oil" and his department's goal is to restore the river to its state before the spill.



"It's going to take time," Heurtel said.



The expert panel does not know how much oil remains in the river. After taking out 43,000 litres of "oily water" and 35 tonnes of absorbent materials used to soak up the oil, as well as using dikes to contain the spill. Michel Rousseau, an assistant deputy minister in Quebec's environment department, estimated that "a good part" of the 100,000 litres had been removed.



The lightest fractions of the volatile Bakken crude the train was carrying evaporated last summer but water-soluble fractions, which are the most toxic, dissolved into a column of water that was rapidly carried downstream, the panel found.



Turbulence in the upper Chaudière, near Lac-Mégantic, favoured a mix of fine drops of oil, water and solid particles, forming an emulsion the consistency of a "viscous chocolate mousse," which covered rocks and the shoreline. Some also settled to the bottom in calmer stretches of the river, the panel said.



Heavy molecules of oil, which are not easily biodegradable, mixed with debris from the fire and other solids, also settled on the river bottom.



Cleanup of the river so far has cost $16 million, an amount the Quebec government hopes to recover through legal actions against Montreal Maine & Atlantic Railway, Canadian Pacific and World Fuel Petroleum.



Heurtel said the legal proceedings are just beginning and it is difficult to say now how they will conclude.



At a news conference beside the Chaudière River, also attended by Lac-Mégantic Mayor Colette Roy-Laroche, other mayors and National Assembly members, Heurtel thanked all those who have contributed to the cleanup of the river and the town. The total cleanup cost has been estimated at $200 million.



The oil spill killed 99 fish and 22 birds, said David Berryman, who chaired the 20-expert committee, adding there appears to be no lasting impact on adult fish. But it remains unclear whether there will be an impact on fish reproduction.



He said fish caught in the river are safe to eat, but not the fish skins or organs. He explained that oil, unlike mercury, does not accumulate in living organisms.



Also unclear is the impact of the spill on the worms, larvae and other small aquatic creatures the fish feed on, Berryman said.

