Meadows Center report reveals threats to world’s lakes, reservoirs

Walter Rast
Walter Rast

Posted by Jayme Blaschke
Office of Media Relations
January 19, 2017

A global study of transboundary lakes and reservoirs led by Walter Rast, a Fellow of The Meadows Center for Water and the Environment at Texas State University, has identified a wide range of threats impacting the world’s freshwater systems.

Rast, who also serves as chairman of the International Lake Environment Committee (ILEC), has found that African lakes collectively exhibited the highest human water security threats, while European and North American lakes collectively exhibited the highest biodiversity threats.

The study, initiated by the United Nations Environment Programme (UNEP), and funded by the Global Environment Fund (GEF) in 2012, is part of an international project called the Transboundary Water Assessment Programme (TWAP).  Transboundary waters, or water systems that are shared by two or more nations, cover more than 71 percent of the planet’s surface. Many continue to be overexploited, degraded or managed in a fragmented manner.

“GEF needed some type of approach for prioritizing the relative threats, and subsequent management interventions, regarding international waters,” Rast said. “Among other goals, the findings from TWAP will be used to produce a global-scale database that will serve as a baseline for future funding priorities.”

The global-scale TWAP effort focused on five major types of transboundary water systems, including lakes and reservoirs, rivers, groundwater aquifers, large marine ecosystems and the open oceans. ILEC was responsible for conducting the Transboundary Lakes and Reservoirs study component, with its final report currently being prepared for global distribution by UNEP.

“Although lakes contain more than 90 percent of the liquid freshwater on the surface of our planet, you will find very few organizations that are solely focused on lakes,” Rast said. “ILEC is one of a few in the world, and currently the leading authority on lakes.”

Lakes and reservoirs comprise a special group of water systems called lentic waters. Lentic water systems pool and store water, in contrast to the flowing waters present in rivers and streams, the latter known as lotic water systems.

“The lentic water systems provide the widest range of ecosystems services to human beings, compared to all other freshwater water systems,” Rast said. “We grow more fish in lakes than other water systems. We also use them as readily-accessible human and agricultural water supplies, recreation, transportation, and hydropower generation, to name a few human uses. They also have major cultural or religious significance to some societies.”

Although lakes contain the vast majority of the liquid freshwater on the surface of our planet, there is very little uniform, global-scale data available for these water systems.

“We [ILEC] found an incredible scarcity of information about lakes,” Rast said. “On a global scale, lakes are just an orphan child.”

ILEC used GIS-based spatial analysis of NASA and USGS databases to develop a list of approximately 206 transboundary lakes and reservoirs that served as the basis for the TWAP study, including 156 lakes in developing countries and 50 lakes in developing countries.

“Because we lacked sufficient data for comparing lakes on the basis of their in-lake characteristics, the relative risks to the TWAP transboundary lakes was based on the characteristics of their surrounding drainage basins, based on the assumption that lakes located in degraded basins would also likely be degraded,” Rast said.

The TWAP Lakes Final Report calculated transboundary lake threats on the basis of the estimated risks facing the lake basin population in regard to human water security and aquatic biodiversity.

“We [ILEC] did not define or identify the “worst lake” in the world during the course of the TWAP study.  This designation must be based on consideration of what is most important to the users of the ranking results,” Rast said. “Such designation is not simply a number-crunching exercise, but rather must consider the perception of the users of a lake, and what they consider important in any given drainage basin, whether it be the size of the lake or its drainage basin, the basin population or density, or the socioeconomic conditions of the basin population.”

Based on the drainage basin characteristics, the TWAP assessment found that African transboundary lakes as a group exhibited the greatest human water security risks, followed by lakes in Asia and South America, while exhibiting lesser risks on the basis of the threats to their biodiversity.

“Lakes are really important freshwater systems, which is why were we were so surprised little was known about them on a global scale,” Rast said. “It is clear the international community must focus much more attention on studying these important water sources.  ILEC, in cooperation with other partners, including The Meadows Center for Water and the Environment, will continue to promote and support such efforts to the maximum extent as follow-up activities are being considered.”

Visit to read the full report and learn more about TWAP.

About The Meadows Center for Water and the Environment

The Meadows Center for Water and the Environment was named following a generous gift from The Meadows Foundation in August 2012. The Meadows Center for Water and the Environment is dedicated to environmental research, stewardship, education and service. It is run by renowned conservationist Andrew Sansom.