David Lavallee travels down the Athabasca River to see firsthand how the search for oil threatens rivers and the third-largest watershed in the world. The development of Alberta's tar sands puts the Canadian water supply at risk. David Lavallee travels down the Athabasca River to see firsthand how the search for oil threatens rivers and the third-largest watershed in the world. The development of Alberta's tar sands puts the Canadian water supply at risk. David Lavallee travels down the Athabasca River to see firsthand how the search for oil threatens rivers and the third-largest watershed in the world. The development of Alberta's tar sands puts the Canadian water supply at risk. David Lavallee travels down the Athabasca River to see firsthand how the search for oil threatens rivers and the third-largest watershed in the world. The development of Alberta's tar sands puts the Canadian water supply at risk.