Sydney's beach wanderers may be in for a treat these evenings as a "flowering of the oceans" including a bloom of sea sparkle heralds the arrival of spring.

Millions of tiny single-cell dynamos, most likely to be dinoflagellates, have been visible as waves break along Manly shores.

Brilliant blue of Manly: Dinoflagellates do their thing. Credit:Saltmotion/Joel Coleman

"It's a good signal of spring in coastal waters," said Iain Suthers, an expert in fish and plankton-like sea creatures at the University of NSW.

Ocean upwellings of nutrients combined with favourable coastal winds and the warming conditions of spring are likely to have prompted the algal-like bloom, Professor Suthers said.