Oil spill a common phenomenon in Malaysia, claims environmentalist

"There are a lot of companies like this, except this one might be too stupid to release so much oil in a short time. Perhaps it is to get rid of extra oil sludge that they can't sell or reuse or recycle,” he said.

Almir also said based on his experience this could have been done around Friday midnight and it reached the treated water around 8am during water treatment plant's regular monitoring time.

“The presence of oil was detected at a very early stage. We are luckier than we thought. Otherwise, the closure could have been longer," he said.

There are provisions in the law that can punish those who pollute the environment.

On Friday morning, a tanker lorry carrying diesel skidded into Sungai Selangor, causing an oil spillage into the river.

The incident forced the closure of four treatment plants. However, they were restarted early Saturday.

Astro Awani reporter’s visit to the site showed that there is no more oil spillage detected but the drain is closed to avoid further residues.