A local Chinese government says it plans to build an environmental monitoring station on a tiny uninhabited South China Sea shoal at the heart of a territorial dispute with the Philippines.

The top official in Sansha City that administers China’s island claims was quoted by the official Hainan Daily newspaper as saying such stations were being built on six islands and reefs, including Scarborough Shoal off the northwestern Philippines.

Beijing seized Scarborough in 2012 after a prolonged standoff with Philippine vessels.

China has since allowed Filipino fishermen to return to the shoal following Philippine President Rodrigo Duterte’s calls for closer ties between the countries.

China insists it has historical claims to almost the entire South China Sea, through which an estimated $5 trillion in global trade passes each year.