Harmful Algal Bloom

Algae bloom in Lake Winnipeg in the Canadian province of Manitoba, with Reindeer Island visible in the lower-right part of the image. Image: contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO.


Harmful algal blooms (HABs) are proliferations of certain noxious and/or toxic micro- and macroalgae and cyanobacteria, regardless of their concentration, with negative impacts on aquatic ecosystems, and human health and wellbeing. HABs are naturally occurring phenomena that are also facilitated by anthropogenic pressures (including eutrophication, habitat modification and introduction of exogenous HAB organisms). HABs constitute a complex global problem that might increase in severity and frequency, and be expanded in biogeographic range, in our changing planet (GlobalHAB).

Facts and figures

Harmful algal blooms occur when colonies of algae grow out of control and produce toxic or harmful effects on people, fish, shellfish, marine mammals and birds. HABs occur naturally, but human activities that disturb ecosystems seem to play a role in their more frequent occurrence and intensity. Increased nutrient loadings and pollution, food web alterations, introduced species, water flow modifications and climate change all play a role. Studies show that many algal species flourish when wind and water currents are favorable. In other cases, HABs may be linked to “overfeeding.” This occurs when nutrients (mainly phosphorus and nitrogen) from sources such as lawns and agriculture flow into bays, rivers, and the sea, and build up at a rate that “overfeeds” the algae that exist normally in the environment. Some HABs appear in the aftermath of natural phenomena like sluggish water circulation, unusually high water temperatures, and extreme weather events like hurricanes, floods, and drought (NOAA).

HABs are natural processes that occur in all aquatic systems and cause worldwide problems with significant economic, socio-cultural, and human health consequences. There is considerable concern that some HABs and/or their associated impacts may be increasing and expanding globally due to a combination of natural and human-driven forcing, including climate change. In the past two decades, improvements in scientific understanding of the complex processes involved in HAB dynamics have contributed to better management of the risks associated with some harmful events (GlobalHAB).

Related content on the Knowledge Portal

Data Source

Publishing institution: European Space Agency (ESA)
ESA's Earth Observation Thematic Exploitation Platform (TEP) is a browser for satellite imagery and specific products on an environmental topic. The TEP platforms are divided into 7 categories: Coastal; Forstry; Geohazards; Hydrology; Polar; Urban; and Food Security. Each platform is a collaborative, virtual work environment providing access to EO data and the tools, processors and Information and Communication Technology resources required to work with them. TEP aims to bridge the gap between the users and the data and tools.
Publishing institution: Airbus Defence & Space
Pleidas, TerraSar-X, SPOT and Elevation data available commercially from airbus, certain sample data sets at various locations available for free.
Publishing institution: Radiant Earth Foundation
The website: https://www.radiant.earth Help and Tutorials: https://help.radiant.earth/ Demos & Use Cases: https://demos.radiant.earth/
Publishing institution: NASA Earth Science Disasters Program
NASA's Earth Observing System Data and Information System (EOSDIS) is a program for archiving and distributing Earth science data from multiple missions to users.
Publishing institution: OceanDataLab
The Ocean Virtual Laboratory is a web platform making satellite and in-situ data for ocean monitoring accessible. It presents one of multiple Syntool Web portals that promote the synergistic use of Ocean Remote Sensing data in a wider context of Oceanic and Atmospheric models or in-situ data. , ESA/SEOM Ocean Virtual Laboratory portal: SAR roughness Sentinel 1: Ocean Color: From Sentinel-2, Sentinel-3 and Meteosat. Chlorophyll: From VIIRS and MODIS Sea Surface Temperature, Sea level, Salinity, Wind, Current, Rain, Mean Square Slope, Sea ice concentration , ESA/DUE GlobCurrent portal: SAR roughness, Ocean Color, Chlorophyll, Sea surface temperature, Sea level, Salinity, Wind, Wave, Current, Rain, ESA SMOS Storm portal: Significant Wave height (SWH) Jason 2 and ALTIKA, SAR roughness Sentinel-1, Wind speed SMOS, SMAP, AMSR2 and ASCAT, wind barbs ASCAT, CNES Aviso'VIZ altimetry portal: Sea Surface Height Anomaly (SSHA) Jason-2 and SARAL, Sea Level Anomaly (SLA) Jason-2 and SARAL, Absolute Dynamic Anomaly (ADT) Jason-2 and SARAL, Mean Sea Level RIse, Sea Level Anomaly, Geostrophic current vectors and streamlines., ESA Sentinel3 Viewer: products from OLCI, SLSTR and SRAL sensors., CNES PEPS Sentinel-1 Ocean Viewer: SAR roughness Sentinel-1, ESA Sea Surface Salinity portal: SMOS salinity, SMAP salinity


Global monthly primary productivity. Image: ESA

A recent study has produced a 20-year time series of primary production by marine phytoplankton, one of the largest fluxes of carbon on our planet. Studying phytoplankton primary production is important because it provides useful information about ocean biology, climate, and global carbon cycle. Observing primary production over long-time scales or quantifying its small variations can help the scientific community to determine carbon dioxide concentrations, as well as the effect of climate variability on these processes. The study uses in -situ measurements and satellite data from the European Space Agency’s (ESA) Climate Change Initiative,

The study assesses global annual phytoplankton primary productivity between 1998 and 2018 and aims at identifying its long-term patterns and its variability with seasons and locations. It uses a global database of in situ measurements of photosynthesis versus irradiance (P-I) parameters and a 20-year record of climate... read more

Publishing date: 11/05/2020

GP-STAR factsheet

Schematic Workflow for the derivation of an exemplary Sendai indicator using crisis information generated from satellite remote sensing (Source: own figure; Copernicus Emergency Management Service (©European Union), EMSN024, EMSN056)
Publishing institution: German Federal Office of Civil Protection and Disaster Assistance

To meet the global challenges, the United Nations adopted several framework agreements, including the Sendai Framework for Disaster Risk Reduction at the Third United Nations World Conference on Disaster Risk Reduction (2015-2030). The framework builds the international reference point for disaster preparedness and focuses on reducing existing and future disaster risks as well as enhancing disaster resilience. In the Sendai framework, seven global targets have been agreed to measure global progress in implementing the framework through quantifiable indicators and to present, compare and evaluate the status and progress uniformly worldwide. The recording of the status and degree of target achievement using the agreed indicators requires the use of various data sources, which must be consistent and comparable in time and space in order to ensure global monitoring.


Algal blooms are indicators of marine ecosystem health; thus, their monitoring is a key component of effective management of coastal and oceanic resources. Sentinel-3 Ocean and Land Colour Instrument (OLCI) imagery provides continuous, high frequency water quality monitoring of coastal waters.

This webinar aims to teach the basics of image processing for ocean colour monitoring. It shows how to access the RUS Service and how to download, process, analyse and visualise the free data acquired by the Copernicus satellites.

The course employs the ESA SNAP Sentinel-3 Toolbox to demonstrate the methodology for the detection and mapping of phytoplankton blooms.

Free advanced webinar from the Applied Remote Sensing Training (ARSET)  programme at NASA.

This webinar series will help to perform advanced image processing of satellite data. It also incorporates the learning about using satellites to track indicators of harmful algal blooms. This will include monitoring water temperature and chlorophyll-a concentrations. Finally,  the information course can be use for reporting around UN SDG 6.

The learning objectives are:

  • Access MODIS and Landsat data
  • Perform image processing of MODIS and Landsat data
  • Monitor water temperature and chlorophyll-a concentrations as harmful algal bloom indicators


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