A research boat (L) and Filipino fishing vessel (back R) anchored near Thitu island in the disputed Spratly islands on April 21, 2017.

The Philippines’ defense minister on Tuesday ordered the military to investigate a report by a United States-based tech firm that hundreds of Chinese vessels were dumping sewage into contested areas of the South China Sea.

China maintains a constant presence of coastguard and fishing boats in the South China Sea to assert its claim of sovereignty, including hundreds in the Spratly islands, where the Philippines, Brunei, Taiwan, Vietnam and Malaysia also have claims.

Simularity, an AI-based satellite image analysis firm, on Monday released public satellite images over a five-year period that it said showed damage caused by untreated human waste from Chinese vessels.

A reef near Thitu island in the disputed Spratly islands on April 21, 2017.

“While we are confirming and verifying these wastes being dumped … we consider such irresponsible acts, if true, to be gravely detrimental to the marine ecology in the area,” Philippine Defense Secretary Delfin Lorenzana said in a statement.

“Despite conflicting claims and interests by states in the South China Sea, all nations must be responsible stewards of our natural resources and environment.”

At a forum on Monday, Liz Derr, Simularity co-founder and CEO, said the waste could threaten fish stocks.

“It is so intense you can see it from space,” Derr said.

The Chinese embassy in Manila did not immediately respond when asked by media for comment on Simularity’s report.

Tensions in the South China Sea have ratcheted up this year, with Manila accusing Beijing of trying to intimidate its coast guard vessels, as well as sending its so called “maritime militia” to crowd out Philippine fishing boats. In May, the Philippine foreign minister demanded in a tweet that China’s vessels “GET THE F**K OUT” of the disputed waters.

China claims almost the entire South China Sea, through which about $3 trillion of shipborne trade passes each year. In 2016, an arbitration tribunal in The Hague ruled the claim was inconsistent with international law.