Watch: Bio-luminescent organisms found at Wellington marina

In the daylight it's simply an unappealing layer of pink slime floating on the water.

But at night the "discoloured smear" on parts of the waterfront in Wellington transformed into a dazzling, glowing blue, caused by bio-luminescent organisms that washed up near the marina.

Wellington woman Sarah Day this week captured video of the stunning effect down at Chaffers Marina - but warns other Wellingtonians not to come looking for it.

"If I was looking for it I would look in areas between things where the water is a bit protected from the waves," she said.

By now the slime had dispersed from where she found it in the marina, but regardless, it was found in a private area that the public don't have access to.

"In a southerly wind it accumulates on the south side of the pier, in behind boats that protect it from being blown away immediately," Day said.

The slime was "around quite a lot" in various places on the waterfront, but not usually as thick as when Day filmed it the other day.

"[It] looks like a discoloured smear on top of the water during the day."

It can most often be spotted after settled weather, with sunny days.

"The winds and waves move it around a lot."

Day said the bio-luminescence was "pretty magical" and appeared much brighter in person than it did on videos or in photos.

According to Te Papa, bio-luminescence occurs at any depth of the ocean and is caused by living organisms experiencing a chemical reaction.

The reaction happens when a substance called a luciferin is oxidised, and the most common coloured reaction is blue.