Amid the rocks, water and greenery at Lower Seletar Reservoir, the blobs of pink stood out.

Not only did they catch the attention of Facebook user Elsa Xu on Oct 5, but they also set off alarm bells for her.

The large clusters belong to an invasive snail species known as the golden apple snail.

In her post on the Nature Society Singapore (NSS) Facebook page on the same day, Ms Xu said she was taking a walk with her daughter along the reservoir when they stumbled across a “significant presence of golden apple snail eggs”.

Expressing her shock, she added: “They are scattered everywhere – along the bank, on the rocks, and even on the reeds. The situation is alarming, and I believe immediate action is needed to address this issue and remove the eggs.”

She added that she has e-mailed national water agency PUB to bring the matter to its attention.

Several photos of the scene captured by Ms Xu show hundreds of bright pink egg clusters speckled across the reservoir’s rocks and vegetation.

In one photo, a plastic bag is seen to be overflowing with snail shells.

According to a biodiversity guide by PUB, the golden apple snail, which has the scientific name pomacea canaliculata, is one of the top 100 most invasive species in the world.