The hazardous pollutant, in the form of black sticky oil, covered up the leaves and stems of mangrove saplings recently planted by the environmentalists on the island.
"Some of the mangrove saplings that we had recently planted withered and died due to it," said Evy R. Syamsir, an environmental activist, here on Wednesday.
He noted that the saplings were planted last week and had already taken root, before the pollutant had a destructive effect on them.
"The black oil has also tainted the rocks, the floating seaweeds and the beaches around the island, which will have a negative impact on the tourism sector," Evy stated.
Meanwhile, Barelang district resident Sukmawati said: "The oil sticks to my son`s shirt, and it is hard to clean."
She was not aware that the clear seawater of Putri Island was contaminated with pollutants.
Marine observer Eddiwan stated that approximately 365,000 tonnes of waste were disposed of in Riau Islands waters.
"The figure comes from the assumption that 10,000 ships passed by Riau Islands everyday and each of them disposed of 10kg of waste in the year 2010," he explained.
Eddiwan noted that the number of ships passing by Riau Islands had significantly risen over the past two years.
"The toxic waste, generated from offshore ship-cleaning activities, cannot dissolve and will eventually reach the shores," he continued.
"A lot of waste substances are not dissolvable, but people treat the sea as a garbage bin," Eddiwan said.
He stated that mangrove plantation was necessary to protect the island from environmental damage.
"The tree and the bacteria living around it can process and dissolve harmful pollutants," Eddiwan added.