This photograph from the International Space Station highlights a late-summer "whiting event" visible across much of Lake Ontario (one of North America's Great Lakes). Such events commonly occur in late summer and are caused by changes in water temperature, which allows fine particles of calcium carbonate to form in the water column. Increased photosynthesis by phytoplankton and other microscopic marine life can also reduce the amount of carbon dioxide in the water column, changing the acidity and allowing calcium carbonate to form. These particles of calcium carbonate cause the characteristic lightening ("whiting") of the water color observed.
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 whiting event on the same day, August 24, 2013.
Editor's Note: A previous version of this story identified the discoloration of the water as a bloom of phytoplankton or harmful algae. Such events can produce stunning color changes, as shown here. However, scientists working on the water in the area provided information to verify that it was instead a whiting event.