National Parks Board (NParks) officers are looking into the cause of hundreds of fish deaths along a stretch of beach in Pasir Ris.

The silver-coloured fishes, as well as several crabs, were spotted washed up at Pasir Ris Park yesterday morning.

Three cleaners were seen along the approximately 150m stretch of shoreline clearing the dead animals into large bags at about 8am.

NParks' coastal and marine director at the National Biodiversity Centre Karenne Tun said that based on preliminary findings, the fish were mainly clupeid (mostly Hilsa kelee), a family of wild fish found in Singapore's coastal waters.

"NParks officers did not observe any dead fish or biodiversity along the surrounding coastal areas along Changi Beach, East Coast Park and Pulau Ubin, including Chek Jawa," said Dr Tun. There were also no reports of fish deaths at the nearby fish farms, she added.

NParks officers will continue to monitor the coastal beaches for anomalies and look into the cause of the fish deaths. In April last year, thousands of fish died in the waters near Lim Chu Kang jetty and in nearby fish farms. Fish farmers in the area sent motorboats out to remove and dispose of the dead fish that had surfaced in the sea.

The warmer weather was said to be the likely cause, as higher temperatures could have resulted in a lack of oxygen in the water.

There was also a mass fish death in 2015, when around 600 tonnes of fish died in a span of two weeks due to a plankton bloom.

A bloom happens when plankton multiply rapidly due to warmer temperatures in the water. Plankton suck oxygen from the water.