The International Boundary and Water Commission (IBWC) said Wednesday that a controversial 700-mile fence along the US-Mexican border may violate the 1970 Boundary Treaty, which resolved all pending boundary differences between the United States and Mexico. Sally Spener, spokesperson for the IBWC, said that impermeable fences on US territory but between existing rivers and levees could violate the treaty by deflecting or obstructing the natural water flow. The treaty established the Rio Grande and the Colorado River as the international boundary between the two countries, and established provisions to avoid the loss of territory by either party as a result of changes to the river's flow due to causes other than natural lateral movement. Spener said that the IBWC is still waiting for the Department of Homeland Security (DHS) [official website] to submit specific proposals detailing the fence's design and location before it can make a final determination. The IBWC is a a bi-national body created by the United States and Mexico in 1889 to administer boundary and water-rights treaties between the two parties.

President Bush signed the Secure Fence Act of 2006 in October 2006. The legislation authorizes the construction of approximately 700 miles of fencing along the 2,000 mile US-Mexican border. Critics of the fence include locals in border communities, who feel that the the federal government has not addressed their concerns that a border fence would interfere with irrigation, harm wildlife, as well as disrupt Mexican consumers and investors that positively contribute to the local economy. The Vatican and the Mexican government have voiced strong criticism of the fence, characterizing it as "inhumane" and an embarrassment that "hurts bilateral relations and goes against the spirit of cooperation needed to guarantee security." The Department of Homeland Security (DHS) says it is scheduled to complete over half of the authorized fence by the end of 2008.