Topic 3e (part 1) - Ocean water quality

Harmful Algal Blooms and coastal pollution can impact aquaculture, tourism and human health. The colour of the ocean is directly linked to the components of ocean waters that determine water quality.

We intuitively understand what might be in water just by looking at its colour. This is something that’s long been investigated by those working on the sea, e.g. fishermen.

Blue ocean water usually contains very little beyond sea water itself, whilst brown waters may be full of sediments and dissolved substances from rivers, or the sea bed. Green water is full of life, in particular, tiny phytoplankton, the sea-dwelling equivalent of plants. These plants provide food for almost the entire marine food web, but they can also produce toxins, or cause anoxia when they form Harmful Algal Blooms.

Ocean colour can be measured from space, and in situ using radiometers. Sentinel 3a has a radiometer on board, the Ocean and Land Colour Instrument (OLCI), which is now measuring the ocean colour for scientists to use to understand water quality.

Optional Mini Task:

You can learn more about Harmful Algal Blooms and how ocean colour validation is conducted by completing this LearnEO tutorial using ocean colour data and the BILKO software. BILKO can be downloaded here

Featured Educators:

  • Dr Gavin Tilstone

Explore the data

EUMETSAT Oceans MOOC Data Viewer

View featured satellites on the satellite tracking app

Don’t forget you can download the video and transcript with the links on the right.


Coccolithophore between Scotland and Norway

Early Sentinel-3 image of coccolithophore between Scotland and Norway

Upsala Glacier

Upsala Glacier in Argentina’s Los Glaciares National Park is pictured in this Sentinel-2A image from 22 January 2016. Taking a closer look at the terminus of the Upsala Glacier, we can see how icebergs have broken off and are floating in the water of the upper reaches of Lake Argentino. The lake’s unique colour is attributed to ‘glacier milk’ – suspended fine sediment produced by the abrasion of glaciers rubbing against rock.

The darker lines following the flow of the glacier are moraines: accumulations of rock, soil and other debris – including glacial milk – that have been deposited by the glacier.”

Baltic Swirls

Captured by Sentinel-3A on 23 June 2016, this image shows an algae bloom in the Baltic Sea. Sentinel-3A carries a suite of instruments to monitor our changing world. This image was captured with its ocean and land colour instrument, OLCI, which provides biogeochemical measurements to monitor, for example, concentrations of algae, suspended matter and chlorophyll in seawater. This information can be used to predict harmful algal blooms, which is particularly relevant in the Baltic Sea where extreme blooms are a significant problem. The health and vulnerability of marine ecosystems is fundamental to our knowledge of ocean productivity and, in turn, fish stocks.

Phytoplankton Bloom in Baltic Sea

A colourful summer marine phytoplankton bloom fills much of the Baltic Sea in this image captured by Envisat’s MERIS on 13 July 2005.

Barents Plankton Bloom

This image is a natural-colour capture of a plankton bloom in the Barents Sea by the Sentinel-2A satellite.

Lake Erie Algae Bloom

Algae bloom in Lake Erie in 2011, taken by Envisat

Algae Bloom

Image from Sentinel-2A taken on 7 August 2015 shows an algal bloom in the central Baltic Sea. The algae is concentrated in locations where the vertical and horizontal water movements in the Baltic Sea generate the best nutrient and light conditions for algal growth, which are then drawn out by the water circulation.

Baltic Bloom

This image of an algal bloom in the central Baltic Sea was captured by Sentinel-2A on 7 August 2015

Eye of an Algal Storm

Sentinel-2A captured this detailed image of an algal bloom in the middle of the Baltic Sea on 7 August 2015. The image, which has a spatial resolution of 10 m, reveals the bloom in exquisite detail as well as a ship heading into the ‘eye of this algal storm’. The ship’s wake can be seen as a straight dark line where the bloom has been disturbed by the ship’s propellers.