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Protecting Waterways from a Deadly Problem

Nutrient pollution emerges as one of the greatest threats to water quality.

In the Chesapeake Bay, large schools of jellyfish scare away swimmers. In the Gulf of Mexico, a 3,000 square mile “dead zone” threatens a multi-billion dollar fishing industry. In Qindao, Beijing Olympics officials had to scoop large masses of green algae out of the water before sailing races could take place. These are all effects of eutrophication---pollution caused when nitrogen, phosphorus and other nutrients enter the water in massive amounts. And it's a problem with which people in both the developed and developing world are becoming frighteningly familiar.

What is eutrophication?

While “nutrients” are usually seen as a good thing, eutrophication is really a matter of “too much of a good thing.” Nutrients entering waterways can come from a variety of sources, such as chemical fertilizers, vehicle emissions, treated wastewater, manure, and septic systems.

Over the past fifty years, eutrophication has increasingly become one of the greatest risks to our water quality. A new set of WRI policy notes provide a global assessment of areas at risk, a description of eutrophication sources and drivers, and a review of policies, actions, and strategies to address this deadly problem.

When too many of these nutrients run off into waterways, they upset the natural balance of aquatic ecosystems. Too many nutrients act like too much fertilizer -- the nutrients feed booming algae populations, which can overrun waterways, block sunlight, and sap the water of its oxygen, creating hypoxic or “dead” zones, fish kills, and ecosystem collapse. Today, over 500 coastal areas are suffering from eutrophication, and 405 of those experience hypoxia, where oxygen levels in the water dip so low that they cannot sustain life.

Nutrient pollution is devastating to communities that depend on ecosystem services like tourism, recreation, and fisheries. For people living alongside eutrophic water, the decaying smell and the toxins released by the algae can irritate eyes, throats, and skin. Recently, Wisconsin state officials had to advise residents near algae-covered lakes across the state to close their windows, avoid walking near the shorelines, and to keep pets away too, as several dogs had died from drinking the water. “It is like living in the sewer for three weeks,” said one resident. “You gag. You cannot go outside. We have pictures of squirrels that are dead underneath the scum and fish that are dead…It has gotten out of control.”

What are the sources and drivers of nutrient pollution?

Most of these chemicals come from agricultural, urban, and industrial sources, and from the burning of fossil fuels. Over-applied synthetic fertilizers run off agricultural fields and leach into groundwater, and animal waste from concentrated livestock operations and fish farms (aquaculture) also find their way into water systems. Municipal wastewater treatment plants, industrial wastewater discharges, septic tanks, raw sewage, and storm runoff are other contributors. Pollutants can also enter waterways through the air. When fossil fuels are burned, they release nitrogen oxides (NOx) into the air which can then redeposit into the water.

The world’s growing population and economy are increasing the demand for food, land, energy, and natural resources, ultimately leading to greater agricultural production, more sewage, an use of fossil fuels. These activities in turn lead to the destruction of “nutrient sinks” like forests and wetlands that traditionally filter excess nutrients out of waterways. The rapid increase in meat consumption is one example -- in China, meat production rose by 127 percent between 1990 and 2002, but fewer than 10 percent of an estimated 14,000 intensive livestock operations have installed pollution controls.

In the United States and European Union, the primary sources of nutrient pollution are typically agricultural sources, while in Asia and Africa the primary source is often urban wastewater. Developing countries have a problem with “point sources” of nutrient pollution: pipes or other outlets that discharge chemicals and sewage. North America treats 90 percent of its sewage, but Asia treats only 35 percent, Latin America and the Caribbean 14 percent, and Africa less than one percent.1

What can be done?

Designing an effective response to eutrophication is a challenge. Pollutant sources are often miles away from the areas they affect, and many different players can share the same watershed. For example, the Chesapeake Bay watershed covers parts of six states, and the Mississippi River watershed includes 31 different states. Preventing nutrient runoff in Corn Belt state can help address the recurring dead zone in the Gulf of Mexico, over one thousand miles away. This fall, a task force dedicated to restoring ecosystems in the Gulf actually met in Iowa.

Despite the geographic challenges, the good news is that these areas can recover. Boston Harbor and the Mersey Estuary in the UK are both showing improved water quality because of better industrial and wastewater controls. The Black Seaonce had recurring hypoxic areas, but has slowly moved into a state of recovery with the reduction of fertilizer use. And New York City still gets its drinking water from the largest unfiltered water supply in the U.S., in the Catskills Mountains, since officials realized it would be cheaper to protect the watershed ecosystem than to pay to purify the water. Today, there is more sensitive land in conservation, better sewage treatment, and more sustainable forestry and farming practices in the area.

In developing countries, basic sewage treatment and improved governance can help immensely. Point sources (pipes and waste outlets) are typically the most controllable sources of nutrient pollution. Strong governance is the greater challenge. Without strong institutional authority, adequate funding, and properly trained personnel to enforce the rules already on the books, there’s only so much that good regulations and policies can achieve.

Policymakers in developed countries must look broadly at agricultural, energy, land use, and public health policies to address the diverse sources of nutrient pollution and design policies to mitigate them. Policies cannot be limited to traditional command-control approaches such as regulatory standards, nor can they focus on one single sector.

Eutrophication, like climate change, is a big picture issue. Its causes stem from our very way of life. We know the policies that would help, but the challenge is in implementation. In the end, it’s really about sustainable lifestyles.

For more information, see the full policy notes:


  1. Martinelli, L.A. 2003. “Element interactions as influenced by human intervention.” In J.M. Melillo, C.B. Field, and B. Moldan, eds. Element Interactions: Rapid Assessment Project of SCOPE. Washington, DC: Island Press. As cited in Howarth, R. and K. Ramakrishna. “Chapter 9: Nutrient Management.” In K. Chopra, R. Leemans, P. Kumar, and H. Simons, eds. 2005. Millennium Ecosystem Assessment (MA). Washington, DC: Island Press. 

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