13 Sep 2017 Story Ecosystems and Biodiversity

What do you know about algal blooms?

Do Algal blooms occur because of climate change?

No. Excess nutrient flows of phosphorus and nitrogen from farms and industry that end up in aquatic systems lead to algal blooms. Too much nitrogen and phosphorus in the water causes algae to grow faster than ecosystems can handle.  Warmer temperatures can exacerbate the problem.

Surely, algal blooms have been around for a long time and do no harm.

This isn’t true. Although harmful algal blooms have been documented for more than a century, recently the number and frequency of cases have drastically increased.

An international research team has analysed the relationship between the amount of phosphorus recorded in 1,500 European lakes and reservoirs, and the growth of cyanobacteria, a toxin-producing microorganism that can be harmful to human health. The results show that 23 per cent of these water masses in Spain exceed the level recommended for recreational waters established by the World Health Organization. This percentage is closer to 50 per cent for Germany and the Netherlands.

Mallard in algal bloom on Lake Menomin, Wisconsin, USA  ©: Aaron Carlson


Algal blooms are associated with mass fish kills, wildlife mortality, and liver failure and irreversible neurological disease in humans. Is that right?

Yes. During a bloom, algae can produce toxins that can render water unsafe and cause fish mortality, or can impact human health through the consumption of contaminated seafood, skin contact and swallow-water during recreational activities. Toxins are usually released when an algal bloom dies off. Water or seafood contaminated with toxins are odourless and tasteless, and toxins cannot be destroyed by cooking or freezing.

Did the US state of Michigan designate its section of Lake Erie an impaired waterway?

Yes. In late 2016 Michigan designated its section of Lake Erie an impaired waterway because of damage to fish and other wildlife caused by harmful algal blooms. 

What’s UN Environment doing about all this?

Adequate access to freshwater and its productive uses require sound legal frameworks and good governance. Through its five-year Freshwater Strategy, UN Environment works together with a range of stakeholders to protect and restore freshwater ecosystems and their services.

Through its Freshwater Ecosystems Unit, UN Environment works to measure and value freshwater ecosystem services, as well as monitor and protect significant freshwater bodies in countries through its role in the water-related Sustainable Development Goals.

Through the Global Wastewater Initiative , a multi stakeholder platform, UN Environment and partners are working to raise awareness of the importance of pollution prevention, and controls at source, as key to reducing the discharge of untreated wastewater into water bodies.

Algal bloom on Lake Binder, Iowa, USA  ©: Dr Jennifer L. Graham/US Geological Survey


Through the Global Environment Monitoring System for Water (GEMS/Water), UN Environment is supporting countries in assessing freshwater quality by providing capacity-building and making public water quality data analyses to support scientific assessments and decision-making.

Surface and ground water quality monitoring data collected is shared through the GEMStat information system, which is hosted by the Federal Institute of Hydrology in Koblenz, Germany.

See our 2016 story on algal blooms.

The UN Environment Assembly, the world's highest-level decision-making body on the environment, will gather in Nairobi, Kenya, from 4-6 December 2017 under the overarching theme of pollution.

Sign the Beat Pollution pledge

More information: [email protected]