Algal blooms in freshwater lakes are becoming more common worldwide

Lakes across the world have seen an increase in algal blooms that strangle freshwater ecosystems, according to an analysis of satellite images from 1982 to 2019


3 February 2022

On September 26, 2017, the Operational Land Imager (OLI) on the Landsat 8 satellite captured these natural-color images of a large phytoplankton bloom in western Lake Erie. According to the National Oceanic and Atmospheric Administration, the bloom contains microcystis, a type of freshwater cyanobacteria. These phytoplankton produce toxins that can contaminate drinking water and pose a risk to human and animal health (skin irritant, respiratory distress) when there is direct contact. A few days earlier, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA?s Terra satellite captured a wider view of the lake. Blooms tend to thrive in Lake Erie during summer, sustained by warm water temperatures and nutrients from farm runoff. This year, the bloom has been ongoing since mid-July. NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Caption by Kathryn Hansen.

An algal bloom in Lake Erie photographed by a Landsat satellite in September 2017

Joshua Stevens/NASA Earth Observatory using Landsat 8 data from the U.S. Geological Survey

Blooms of algae that strangle freshwater ecosystems are occurring more often in lakes across most of the world, according to the first study to map their incidence globally.

An algal bloom is the rapid build-up of algae in a body of water after excess nutrients, such as nitrogen or phosphorous, pollute the ecosystem – often as a result of fertiliser use on farms. The bloom can harm other organisms, including fish and insects, by blocking out light, …