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n immediate restoration of Bengawan Solo river basin in Central Java is urgently required as the river is in a critical condition, an environmentalist says.

Bengawan Solo is one of five highly polluted river basins in Indonesia along with Brantas in East Java, Ciliwung in Jakarta, Citarum in West Java and Musi in South Sulawesi.

Green Society Forum director Wasisto Daru Darmawan said this conclusion was based on a study of Bengawan Solo watershed that was carried out from April this year.

Biota samples were taken from the bed of the Bengawan Solo in seven regencies in the Greater Surakarta area, encompassing Surakarta, Boyolali, Sukoharjo, Karanganyar, Wonogiri, Sragen and Klaten.

The observation, using a method called biotilik, also involved 50 students from seven schools in Greater Surakarta.

The biotilik is a water quality monitoring technique which can provide more detailed information by observing the impact of water quality degradation resulting in changes in the river habitat.

The condition of the river habitat is usually indicated by water biota living in the river.

Some biota can only live in places where water pollution is low and some can live in places with high pollution levels.

'€œBased on observation by the students, many biota can live in places where water is heavily polluted, such as worms and larva,'€ said Wasisto, who was speaking during the commemoration of the provincial-level World Environmental Day in Surakarta recently.

Lab analysis also showed that water in the Bengawan Solo contains heavy metals, such as chromium, copper, lead and zinc .

'€œWith the naked eye, water pollution is at a critical level, as seen from the brownish color,'€ said Wasisto.

He said the action taken so far to improve the condition of Bengawan Solo was limited to mitigation efforts, such as addressing floods by relocation, while action to deal with the causes of the critical condition of the basin have not yet come fully online.

Methods used to deal with the Brantas River, which have been car ried out for the past eight years without a pause, have only reduced the pollution level by 15 percent.

So, the time needed to restore the Bengawan Solo could be longer, given the relative size and length of the two rivers.

The Brantas basin is around 11,800 square kilometers (km) and the river stretches for around 320 km, while Bengawan Solo basin covers around 16,000 square km and the river stretches for 600 km.

'€œThe time needed to restore the Bengawan Solo basin could be double. If it takes eight years to restore 15 percent of Brantas,therefore restoring 15 percent of the pollution level of Bengawan Solo could take dozens of years,'€ said Wasisto.