JOHOR BAHRU, Jan 11 — Dredging is among the alternatives that can be considered as a recovery measure following complaints from fishermen on Sungai Sayong Pinang in Kota Tinggi which is getting shallower following the incident of a bund pond burst from sand mining activities in October last year.

Universiti Teknologi Malaysia (UTM) Campus Sustainability Centre director Prof Dr Mohd Fadhil Md Din said the river’s shallowing was due to silt (sediment) from the mining activities entering the river area in large quantities, forming thick deposits.

“Dredging is not a single solution, but it can be part of a recovery plan, especially to restore the river’s depth, reduce the risk of repeated shallowing and restore ecological functions,” he told Bernama.

However, he said dredging needs to be carried out in a targeted and controlled manner, accompanied by a strict sediment management plan so as not to trigger a new surge in turbidity.

The pollution incident that occurred on Oct 31 was the worst recorded involving water supply sources in Johor, affecting more than 292,000 accounts including in the Kota Tinggi, Johor Bahru, Pontian, Gelang Patah and Kulai areas.

The situation previously caused more than a ton of fish such as baung, lampam and jelawat to die and float in the river, thus causing about 150 fishermen to lose their livelihood.

Yesterday, fishermen in Kampung Orang Asli Sayong Pinang, Kota Tinggi complained about their income and river catch declining, in addition to lamenting the condition of Sungai Sayong Pinang near their village which is becoming shallower to only thigh level.

The situation forced local fishermen to change their fishing routes by moving between the two main rivers, namely Sungai Linggiu and the upstream area which takes two to three hours to travel, while waiting for Sungai Sayong Pinang to recover.

Mohd Fadhil said the surge in Sungai Johor’s turbidity to 37,400 (Nephelometric Turbidity Unit), almost 94 times higher than normal levels last October, would not only affect the water supply and cause fish deaths, but would also leave long-lasting silt deposits on the riverbed.

He said that although the river’s turbidity rate could drop within a few days after the pollution was stopped and the Linggiu Dam was released, the fine sediment that had settled would not disappear in a short time.

“This silt usually settles in shallow areas, fish cages and slow-moving riverbeds. It does not ‘disappear’ on its own. Without large flows or physical intervention, it can remain for weeks to months,” he said.

He said continued sedimentation would cause the river to become increasingly shallow, thus increasing the risk of local flooding, disrupting small boat navigation, as well as affecting fish habitat and the livelihood of river fishermen.

“When the silt layer covers the bottom, fish breeding areas will be lost, benthic population will decline and sensitive species will move upstream. This will directly affect cage fishermen and Orang Asli communities who depend on the river,” he said. — Bernama