"Sea sparkle" is a large bloom of marine algae which is mostly seen in June, July and August. It can also be spotted during spring, summer and autumn when there's a lot of agricultural activity which leads to more nitrogen that the organisms need to grow.

The night-time spectacle has been observed across the Mid North Coast at Black Head, Port Macquarie, South West Rocks, Hat Head and as far north as Coffs Harbour.

It has also been spotted further south at Manly and down on the South Coast of NSW.

Port Macquarie local Tania Williams said seeing bioluminescence at the Port Macquarie Marina on January 1 was "a treat".

"It was lovely," she said.

David Finlay, an expert who runs the Bioluminescence Australia Facebook group, said the widespread phenomenon is rare but not unusual.

"We see this up the east coast of Australia a couple of times a year, it's rare but not hugely uncommon," he said.

"Noctiluca scintillans is an algae and it's blooming at the moment due to the intense rainfall that washes nutrients off the land which goes down into rivers and bays.

"The nutrients then feed the food sources of the plankton that the noctiluca feeds on."

Mr Finlay said the algae is close to the surface at the moment in search of food.

"What we're seeing at the moment is a bit of a bloom cycle," he said.

"The algae feeds on the plankton, populates and then they bloom on top of the water when they're running out of food. They float to the surface and use the tides and wind to get blown around to different locations where there's more food."

During the day the algae looks like a "pink scum" on the water's surface and is quite distinctive, however it will glow when disturbed by a wave breaking or a splash in the water at night.

It's a chemical reaction in the algae which causes it to emit light.

Mr Finlay said there's no telling on how long the bloom will last.

"We have multiple pockets of blooming at the moment and it's quite widespread," he said.

"You never know [how long the bloom will last], it entirely relies on the wind direction. If we get westerly winds it will blow it further out and we won't see it congregate on our beaches."

The Bioluminescence Australia Facebook group consists of members from across Australia posting updates on where to find the bright phenomenon.

"There's always posts on there where blooms have been spotted and where people should look out for it," Mr Finlay said.