A week after authorities discovered a refined petroleum product — possibly gasoline — leaking into the Popo Agie River in Lander, the U.S. Environmental Protection Agency began building a wall to contain the spill, according to the City of Lander's Facebook page.

A concerned citizen reported smelling gasoline fumes coming from the river last Tuesday evening. Lander police and firefighters responded to the scene, located on South Main Street. The EPA and Wyoming Department of Environmental Quality took over the scene.

The City of Lander on its official Facebook page said the wall will have wells on the upstream side to contain gasoline products being pumped out of the soil. Construction on the wall was announced Tuesday morning.

However, Wyoming DEQ Public Information Officer Keith Guille said it's too early to say whether to substance is gasoline. It's also unclear if the petroleum substance is coming from a Maverik gas station near the river.

Dye is being placed in the gas station's tanks to determine if it is the source of the spill.

Long-term environmental impacts from the spill are unknown.

A call to the EPA was not immediately returned, but the plan of action for the incident includes removing and halting the flow of gasoline into the river.