The private group that wants to build its own southern border wall next to the Rio Grande in Texas won’t begin construction until the U.S. government certifies the project won’t worsen flooding.

The agency that oversees the river under treaties signed with Mexico has asked the group We Build the Wall to halt construction until it submits more information about the project so the commission could study it.

We Build the Wall’s founder, Brian Kolfage, said Tuesday that the group won’t build until it has the approval of the agency, the International Boundary and Water Commission.

The group had announced on Facebook that it was starting to build a barrier on 3.5 miles (5.6 kilometers) of private land in South Texas.