While acknowledging the danger of diverting huge amounts of freshwater, the DFO said that much remains unknown about the nature and extent of fish loss when river levels drop.
There is "limited biological data available for the Lower Athabasca River," the study said.
Missing, for instance, are baseline data on the size of the fish population, where they breed or how much water is needed to keep them alive.
"They have no idea what the ecological thresholds are," Donahue said. "If we're interested in protecting the Lower Athabasca...you need to get the foundational science that allows you to tell when the river is going to be harmed."
The scientists called for a "well designed monitoring program" to "address both the need for ongoing monitoring data and important data gaps identified."
DFO also urged more research on the effect of global warming on water levels.
Maas said the lack of science should not stall action. "That cannot be an excuse for not putting in place a cutoff now."
Once in a Hundred Years
"It's not going to cause significant harm to...the oil sands industry," Maas continued.
The cutoff level being proposed by scientists is 87 cubic meters per second. At that flow, mining companies would need to stop withdrawals from the river and rely on stored water.
According to the science, that would occur about once in hundred years.
Because of that "we see very little in the way of barriers to just moving this forward," Maas said, adding that there should be a "robust research and monitoring process" established to revisit the cutoff limit "when new and better data arises."
Image: University of Alberta