Barack Obama, the US president, is to make a final decision on the construction of a $7bn extension to Canada's Keystone pipeline to refineries in Texas.

Environmental groups that helped elect the president say that the project is a threat to US farmland and to the Midwest region's largest aquifer - which nearly two million people depend on for drinking water.

Meanwhile, labour unions, who also supported the president, are rallying behind the project due to its promise of thousands of badly needed construction jobs.

Other people who support the extension say that the US needs the pipeline to secure energy dependence.

Al Jazeera's Tom Ackerman reports from Washington.