Filipino fishermen towed Chinese-marked buoys back to shore after seeing them near Scarborough Shoal, Philippines officials said July 26.

According to Reuters on July 26, after three months confrontation with Philippine Coast Guard ships, China seized control of the rocky outcrop in South China Sea in 2012, in order to prevent Filipino fishermen from getting near their traditional fishing grounds.

Filipino fishermen said they had found three long, orange containment booms, used to control oil spills, floating about four kilometers off Scarborough Shoal. It was the first time fishermen there found such devices.

“The buoys have Chinese markings,” one of the fisherman said. “The markings showed the company that manufactured it. It even has phone numbers.”

The fishermen said they towed the buoys back to Masinloc to show officials there and turned them over to the coast guards. The fishermen said they did not know why the buoys were there because there was no sign of any oil spills.

Desiree Edora, the mayor of Masinloc town in Zambales, confirmed the police has started investigation on the buoys.