Story highlights Raw sewage has been reported in the Tijuana River, Tijuana River Estuary and Imperial Beach, California

(CNN) With millions of gallons of raw sewage spilled into the Pacific Ocean surface and onto the shores of southern California, officials in the United States and Mexico have launched a bi-national investigation into the spill that apparently originated in Mexico.

The spill was first spotted in early February along the beaches of San Diego, California down through Tijuana, Mexico, according to the International Boundary and Water Commission. The IBWC is a joint government agency responsible for brokering water treaties between the two countries.

Agency commissioners agreed to investigate the matter after receiving reports about sewage originating in Mexico that affected the Tijuana River, Tijuana River Estuary, and coastal waters at Imperial Beach, California.

"This is the worst spill we've had in over a decade," Imperial Beach Mayor Serge Dedina told CNN affiliate KSWB . "More than 143 million gallons of raw sewage were discharged into the Tijuana River, which flowed through south San Diego, into Imperial Beach (causing) closed beaches from the border all the way to Coronado."

Sewage spill report from #IBWC--143 million gallons spilled into TJ Rver starting on 2/6/17. This is why @WILDCOAST @SurfriderSD are needed. pic.twitter.com/P4gySzlxEu — Serge Dedina (@sergededina) February 25, 2017

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