The 1% figure is probably accurate for annual flow, but the critical time period is really the winter flow of the river. I think David Schindler has addressed the issue of company withdrawals then being somewhere between 7% and 9% of the flow of the river. That's the critical period, and that's the critical issue for water withdrawals on the Athabasca River--it's during wintertime.
On June 11th, 2009. See this statement in context.