SINGAPORE - A nature guide on a visit to Sungei Buloh Wetland Reserve was shocked to see three men allegedly poaching shellfish on Sunday (Dec 3).

Mr Ben Lee, a full-time nature guide at Nature Trekker, told The Straits Times on Monday that he saw three men scooping shellfish into large plastic bags at around 5.20pm.

Mr Lee, 54, said the three men appeared to be digging purposefully for the creatures and continued in earnest for about half an hour. One looked to be in his late 40s and the other two were in their 20s.

Mr Lee, who has visited the reserve for around 20 years, notified the National Parks Board, and an officer arrived soon after.

The officer confiscated the items from the three men, said Mr Lee. Meanwhile, he stood at the bridge blocking off the exit with five or six other people who were with him.

He said the men had most likely dug up the creatures for personal consumption, or "for sale to whoever is interested".

This is not the first time Mr Lee has tipped news organisations off about improper activity in Singapore's parks and reserves.

In 2015, he told ST about a couple and a young child in a kayak at the same reserve.

Canoes and kayaks are not allowed in the area, which is home to wild saltwater crocodiles.

"A nature reserve is a place for the preservation and protection of wildlife and such illegal activity should not be allowed to happen," he said.

"It's a place where you leave nothing but footprints, take nothing but photographs. The taking or removing of shellfish is considered illegal and is within the ambit of the law."

NParks acting group director for conservation Adrian Loo said on Tuesday (Dec 5) that officers were at the scene immediately after they were alerted and had stopped the men involved.

The collected shellfish were returned to the mudflat, he said, adding that the board is investigating the incident and will take appropriate action.

"Our nature reserves and parks are habitats for our rich biodiversity, and activities such as poaching can be detrimental to our ecosystems as they may disrupt the ecological balance," Dr Loo said.

"We would like to remind members of the public that removing animals and plants from nature reserves and parks is not permitted, and seek their cooperation to refrain from doing so. Signs are prominently displayed to inform the public of this."

Under the Parks and Trees Act, those who remove, capture, cause disturbance or displacement of any plant or animal, may face a fine of $5,000 (if the act was committed within a park) or $50,000 (if committed within national parks and nature reserves).

There were 73 notice of offences issued for poaching in parks and nature serves so far in 2017, NParks said.

Of these, seven were issued for poaching at Sungei Buloh Wetland Reserve. Most of the cases were for illegal fishing or for possessing or using fishing gear.

Members of the public who encounter such incidents can alert NParks staff on the ground or call the NParks helpline at 1800-471-7300.

Correction note: This article has been edited for clarity.