Sahabat Alam Malaysia (SAM) said Sungai Kerian was suffering from serious erosion issues that had not only affected the many aquaculture ponds located along the riverbanks but also the water quality.

Riverbank erosion can cause sedimentation, changing the course of a river, reducing its water carrying capacity and in the long term, may cause stronger stream of waters, which would impact fishing in the river.

In a statement, SAM president Meenakshi Raman said the main culprits were the large boats traversing the river, creating large waves and causing the walls of the river to deteriorate to worrying levels.

These large boats, which are mainly transporting fish from the sea to a landing jetty at Ban Sungai Tok Tuntong, Nibong Tebal, exceeded the “carrying capacity” of the river, she said.

“Fishermen have raised this issue to the authorities, saying that if large boats continue to use Sungai Kerian, the situation would become worse.

“If there are no natural barriers or strong retaining walls to prevent the collapse of the riverbank, it would render it unstable. The Irrigation and Drainage Department and the Penang government must step in immediately,” she said.

Sungai Kerian is currently being considered as a raw water source by Penang, as the water demand in the state has increased over the years.

Sungai Muda, which flows through Kedah and Penang, supplies 80% of water in the state, but this is only expected to last until 2025 as the water from the river is expected to dwindle by then.

The idea to extract water from Perak began in 2009 by pumping water out of Sungai Perak and channelling it to Sungai Ijok, also in Perak up north.

Sungai Ijok, in turn, is a tributary of Sungai Kerian which is shared by Penang, Perak and Kedah. Penang, through its Water Supply Corporation (PBAPP), would then build a water treatment plant at the Penang side of Sungai Kerian.

The plan was approved by the federal authorities in 2012 but it never took off. Officially called the Sungai Perak Raw Water Transfer Scheme, the 14.8km water tunnel was expected to cost RM2 billion.

However, the Perak government had opposed the idea, demanding Penang pay for treated water from Perak instead.