Is there a plankton bloom heading your way?


The summer months in the UK often create ideal conditions for plankton blooms. Warm weather, increased sunlight and high level of nutrients at the sea surface provide the perfect growing conditions. Blooms can also be triggered by low water turbulence and changes in salinity from increase in freshwater input from heavy rainfall.

Typically they produce a brown ‘froth’ on the surface which can be mistaken for sewage. Plankton can sometimes increase so rapidly they turn the sea red, green or brown due to the chlorophyll they contain.

A “red tide” is a term used to describe a harmful algal bloom. The bloom may deplete oxygen in the waters and release toxins that may cause illness in humans and other animals.

Plankton blooms are natural events but they can be indirectly linked to human activities. The majority of blooms are harmless to the marine environment but some can be toxic, however, blooms of toxic algae are rare in UK coastal waters.

If you see a suspected algal bloom it is advised to keep pets and children out the water and avoid skin contact with the water or algae.

To report a bloom to the Environment Agency call the Environment Agency incident hotline (24 hour service) 0800 80 70 60

Prepared by Hannah Jackson, Environmental Scientist

Image acknowledgements:
Red sea at Babbacombe image cc-by-sa/2.0 - © Derek Harper -
Brocken Inaglory [CC BY-SA 3.0 (

Like this? Sign up for our newsletter



Natalie Frost

Team Leader


+44 (0) 2380 711 850