Following President Barack Obama’ rejection of the Keystone XL tar sands pipeline, Canadian oil producers are seeking a new way to keep oil flowing south. The new plan? To send oil tankers and barges down the coasts and the Mississippi River.

The National Resources Defense Council released a press release, highlighting their concern about heavily increased traffic in America’s waters, stating, “Under their plan, tar sands tankers and barges traveling U.S. waterways could skyrocket from fewer than 80 to more than 1,000 a year—dramatically increasing the chance of devastating spills.”

The NRDC report stated that spills could put the Pacific and Atlantic coastlines at risk for costly spills with no known effective cleanup technology. The Mississippi River could see as many as 130 tar sand barges per year, though it currently sees little traffic.

“Canadian oil producers have a scheme to flood us with dangerous tar sands oil. Their hopes to send hundreds of millions of barrels of tar sands oil into U.S. waters are truly alarming. We can’t let them endanger American livelihoods, our most iconic and threatened species, or our beautiful wild places with these irresponsible plans,” said Joshua Axelrod, lead author of NRDC’s report.

The Keystone XL Pipeline was rejected partially due to environmental concerns as well.