You probably don't know this, but this week's been pretty big for nature enthusiasts.

Saturday, May 20 through Sunday, May 28, this year, was designated by NParks as Biodiversity Week, with a whole bunch of activities happening to encourage the public to take an interest in our nation's flora and fauna.

Which, if you haven't realised, Singapore actually has a ton of — from endangered red junglefowl, to Atlas moths, and even never-seen-alive T. Rex ants, just to name a few recent examples.

Among the many things happening this week is Bioblitz, a round of intensive surveys in various parts of Singapore by field researchers and volunteers. This process is instrumental in information gathering for habitat enhancement work and wildlife conservation efforts.

Here's one round that was done by one Vincent Choo, at Sisters' Island Marine Park, for instance:

On an earlier round of surveys at Sisters' Island, another group of researchers were in for a treat — a pod of wild dolphins decided to join them in a not-so-common recorded Singapore sighting.

Here's a short video clip taken by one volunteer in the group, Heng Pei Yan, who posted it to Facebook on Sunday, May 20:

As the group was quite far away, though, Heng was regrettably unable to identify their exact species.

But it could've been a similar group spotted by a person who commented on Heng's post, claiming that she saw three nearby, along the coast of Lazarus and Kusu Islands on Thursday, May 18:

Heng told Mothership.sg that the dolphins were swimming around nearby and after that video, which was the only footage she took, her group did not spot them surfacing, but could still hear their clicks — the sound they make to echolocate and "see" underwater.

Dolphins are occasionally sighted in the waters of this region, but just like this encounter, it can be a rather fleeting experience, and so not too easy to record: