A DECLINE in oxygen levels could cause prawns to swim to a riverbank.
Among possible reasons are pollutant run-off from land during a downpour and sediment being transported upstream during high tide.
Aquatic, coastal and marine ecology expert Dr Harinder Rai Singh said these could lead to increased demand for oxygen by organisms living in water.
“The presence of organic and inorganic chemicals, as well as organic matter from the estuary, will also affect oxygen demand.
“For freshwater prawns, the ideal level of dissolved oxygen is between 5 and 7 mg/L.
“They can live in turbid waters, but this is not optimal,” he told StarMetro.
Boatmen in Banting, Kuala Langat, Selangor, had raised concerns about the “udang mabuk” (dazed prawns) phenomenon.
They had noticed that the prawns were less active and had swum closer to the riverbank last month.
Water quality specialist Dr Zaki Zainudin said water downstream of Sungai Langat was at Class 3, as classified under the National Water Quality Standards (NWQS).
“The optimal Class 1 water level is usually limited to remote regions where there is minimal development,” he said.
According to the NWQS, Class 3 water requires extensive treatment and is suitable for tolerant species and livestock while Class 4 is only for irrigation.
Zaki stressed that a lower oxygen level would adversely impact the more sensitive species, leaving only the stronger ones to survive.
“Pollutants such as heavy metals and hormones can accumulate in the organism’s tissues and even alter its behaviour,” he added.
Global Environment Centre director Faizal Parish raised concerns about industrial facilities along Sungai Langat.
“There have been many complaints about pollution caused by these factories,” he said, adding that more testing should be done to identify the source of pollution, if any.
Already a subscriber? Log in
Get 20% OFF The Star Digital Access
Cancel anytime. Ad-free. Unlimited access with perks.
