Incorporating Climate Change into TMDL Decisions for Lake Champlain

Jessi Kershner
Posted on: 5/28/2013 - Updated on: 3/02/2020

Posted by

Rachel Gregg

Project Summary

Lake Champlain, located between the Green Mountains of Vermont and the Adirondack Mountains of New York, has historically suffered from problematic blue-green algae blooms that are dangerous to the health of humans, fish, and wildlife. The blooms are primarily caused by excess non-point source pollution entering the lake, which is likely to be exacerbated by climate impacts such as changes in precipitation and flashier storms. In light of this threat, the Conservation Law Foundation began investigating existing regulatory policies and the ways in which they could be revised to limit algal blooms under future climate change. This case study is also part of a Climate Adaptation Toolkit, developed in partnership between EcoAdapt and Freshwater Future.


Lake Champlain has a pollution problem. The lake – situated between the Green Mountains of Vermont and the Adirondack Mountains of New York – suffers from problematic blue-green algae blooms (also known as “pond scum”). When environmental conditions are just right – the algae prefer warm, slow-moving water enriched with nutrients like phosphorous or nitrogen – blue-green algae can grow fast, creating scum layers or floating mats which, in addition to being unsightly, are dangerous to human, fish, and wildlife health. In Lake Champlain, the primary culprit causing these massive blooms is excess phosphorous.

Pollutants such as phosphorous enter a lake from two types of sources: point sources – clearly identifiable sources like a pipe or ditch that flows directly into the lake – or non-point sources, which are more diffuse. With non-point source pollution, pollutants may be deposited into lakes and water bodies directly by wind or rain, or they may be picked up by rainfall or snowmelt moving over the ground and carried into lakes and water bodies that way. In Lake Champlain, excess phosphorous mainly comes from non-point sources like agricultural and urban runoff, although sewage treatment plants also contribute.

People have been combating the Lake Champlain pollution problem for a number of years. In 2002, the states of Vermont and New York jointly developed a Total Maximum Daily Load (TMDL) for the lake, which was approved by the U.S. Environmental Protection Agency (EPA). A TMDL describes the total amount of a pollutant – in this case, phosphorous – that can be put into the lake but is still considered safe for people, fish, birds, and other wildlife. Both point and non-point source pollutant amounts are used to calculate the TMDL, but while point source pollution amounts are relatively easy to determine, non-point source pollution is not.

In order to calculate the amount of non-point source pollutants, the EPA uses watershed models based on how much precipitation (rain and snow) falls in a single year. In the case of Lake Champlain, 1991 was chosen as the representative year and used to determine the total non-point source pollutant amount. However, since 1991 there has been a trend toward wetter years overall and more intense storms that produce higher flows. More precipitation and higher flows mean more polluted runoff, whether it’s through erosion from a farm field with layers of fertilizer or from a construction site. By using precipitation numbers that were already 10 years old and ignoring long-term trends in precipitation and storminess, the 2002 TMDL was likely to grossly underestimate the amount of non-point source pollution. In addition, future climate projections including warmer temperatures, changes in precipitation, and increased frequency and intensity of storms would likely exacerbate existing conditions. Based on these concerns, staff at the Conservation Law Foundation (CLF) began reviewing the literature to find support for appealing the TMDL.


In reviewing the literature, the CLF found a 2008 EPA publication looking at climate change and the water cycle, and ways the EPA would need to adjust its regulatory program (including the TMDL) to account for these changes. In particular, the paper talked about the impact of global warming on precipitation and how it was likely to make preexisting problems, such as non-point source pollution, worse. However, in order to repeal a decision that has already been made, the CLF needed to find evidence demonstrating that the EPA knew or should have known about climate change impacts back in 2002. In their researching, the CLF found that the U.S. government had been funding climate change research since at least the 1980s, including an interagency work group that had been developing different scenarios of climate impacts on water and other important resources.

After finding enough support for repealing the Lake Champlain TMDL, the CLF filed a lawsuit against the EPA in 2008. In January 2011, the EPA rescinded their approval of the Vermont portion of the Lake Champlain TMDL, due in part to the predicted effects of climate change on lake water quality.

Outcomes and Conclusions

As a result of this lawsuit, the EPA has initiated a nationwide study of the relationship between potential climatic changes and increasing non-point source pollution. They plan to look at how different pollution control techniques (e.g., conventional practices vs. green infrastructure) work under changing climatic conditions. Lake Champlain will be included in the nationwide study and the results will be factored into the new TMDL.

The Vermont Agency of Natural Resources and the EPA are also working on an extensive community outreach campaign to figure out what’s happening in terms of actual on-the-ground pollution control, what ideas people have to do more, and discuss what’s working for folks and what’s not. The CLF and others hope the result of all this discussion and research will be a new TMDL that is truly comprehensive – one that gets the region on a path toward controlling pollution and a clean and healthy Lake Champlain far into the future.


Kershner, J. M. (2012). Incorporating Climate Change into TMDL Decisions for Lake Champlain [Case study on a project of the Conservation Law Foundation]. Product of EcoAdapt's State of Adaptation Program. Retrieved from CAKE:… (Last updated October 2012)

Project Contact

Anthony IarrapinoStaff

Affiliated Organizations

Since 1966, Conservation Law Foundation has used the law, science, policymaking, and the business market to find pragmatic, innovative solutions to New England’s toughest environmental problems. Whether that means cleaning up Boston Harbor, protecting ocean fisheries to ensure continued supply, stopping unnecessary highway construction in scenic areas, or expanding access to public transportation, we are driven to make all of New England a better place to live, work, and play.


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