Plankton bloom in Lake Ontario.
This photograph taken by an astronaut on the International Space Station highlights a late summer plankton bloom across much of Lake Ontario, one of North America's Great Lakes.
Microscopic cyanobacteria, or blue-green algae, can reach such large concentrations and color the water to such an extent that the change is visible from orbit.
Harmful algal blooms, or HABs, have been observed in all of the Great Lakes--particularly Lake Erie--and are caused by a variety of factors, including: changes in precipitation; drought; invasive species (quagga, zebra mussels, Asian carp); nutrient loading from runoff and sewage (nitrogen and phosphorus); and warmer than average temperatures. In addition to reduced water quality and human health concerns, algal blooms can also lead to hypoxia--a reduction of oxygen in the bottom waters that kills large numbers of fish and other aquatic life.
Lake Ontario--like the Great Lakes Erie, Huron, and Superior--is roughly divided between the United States and Canada. The USA side of Lake Ontario has its shoreline in the state of New York, while its Canadian shoreline lies within the province of Ontario. The city of Kingston, Ontario, is visible near the Saint Lawrence River outflow from the lake. Several other landscape features of New York State are visible in the image, including the Finger Lakes region to the west of Syracuse. To the northeast of Syracuse, the dark wooded slopes of the Adirondack Mountains are visible at image upper left. Patchy white cloud cover obscures much of the land surface to the west of Lake Ontario.
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite captured an image of the same bloom on the same day, August 24, 2013.