The (Waste)water Cycle: Sewage Treatment in the Lake Champlain Basin
October 2026 Lake Look Column
In grade school we learn about the natural water cycle and its familiar parts: precipitation, surface runoff, evaporation, and condensation. Human engineering has created a connected cycle that loops some of that water through taps and drains in homes and other buildings. Wastewater is collected and treated before being released back into water bodies such as Lake Champlain which provide drinking water, wildlife habitat, and opportunities for recreation. How does the offshoot “wastewater cycle” from flush to tap interact with the natural cycle, how has treatment changed over time, and what does that mean for water quality?
Wastewater treatment facilities are the major hub for the wastewater cycle. When water from a flush or drain enters these plants, a series of treatment processes transform sewage into clean water. First comes mechanical screening that removes larger objects, followed by settling that separates heavier materials from the water, filtration that sieves out smaller particles, aeration that promotes bacterial breakdown of leftover material, and finally disinfection to kill harmful organisms. What’s left is water that is legally permitted to be discharged into lakes and rivers.
Wastewater infrastructure is easy to ignore when all is going well and easy to vilify when problems arise. When we drain a sink or flush a toilet, we don’t usually consider where the water goes. But when cyanobacteria blooms close beaches, fingers are often pointed toward wastewater treatment facilities. Are these plants working as designed? Can they be improved? Or is something else happening that needs a different solution?
Wastewater is a source of phosphorus and other nutrients—if sewage did not pass through treatment processes, the lake would receive significantly higher phosphorus loads than it does now. In the past, before modern wastewater treatment technology was in place, urban portions of the lake were the most polluted. Marshall Leighton’s 1905 Preliminary Report on the Pollution of Lake Champlain, issued on behalf of the U.S. Geological Survey, concluded that sewage discharges were “a growing menace” and that safeguards should be adopted to preserve the lake as a water supply. The New York Conservation Department’s 1929 Biological Survey of Lake Champlain also noted high nutrient and algae levels in Burlington and Plattsburgh.
Modern technology has reduced the share of phosphorus that wastewater facilities contribute to the lake. According to the Lake Champlain Basin Program’s 2024 State of the Lake Report, wastewater treatment facilities accounted for about 6% of the annual phosphorus load entering the lake, compared to 38% from agricultural land and 16% from developed land. The relatively low share of phosphorus from wastewater is a testament to decades of facility upgrades under the federal Clean Water Act as well as state requirements like phosphorus detergent bans and other pollution reduction requirements that the Lake Champlain Committee (LCC) has advocated for since the 1960s. For phosphorus loading, advances in wastewater treatment have reached the point that further meaningful reduction is often prohibitively expensive, and it is more cost efficient to pursue phosphorus reductions from other sources, such as agriculture and stormwater runoff.
These days, it’s often the combination of wastewater and stormwater that leads to water quality challenges and beach closures. Older combined sewer systems collect sewage and stormwater in one pipe, and both waste streams flow to the wastewater treatment facility. When high flows caused by too much precipitation exceed the capacity of the system, untreated wastewater spills out into lakes and rivers. This is called a combined sewer overflow, or CSO event. In a related problem, stormwater systems that are designed to be separate from the sewage treatment system may receive wastewater due to unsanctioned connections or inadequately separated infrastructure. Determining exactly what is occurring underground can require a lengthy process to detect and eliminate these conditions.
With heavy rains increasing due to climate change, more overflow events occur and more phosphorus is conveyed into our waters from these dated systems. It also means that more of everything else found in raw sewage, such as E. coli, parasites, and other pathogens, enters our waters, which can pose immediate and acute water quality hazards.
To address this, municipalities throughout the Lake Champlain basin have been upgrading their facilities, detecting illicit sewer hookups, disconnecting combined sewer systems, and endeavoring to minimize CSO events. It is complicated and expensive work that requires significant investment from communities as well as access to federal and state water pollution control funds.
What can you do to get involved with work to improve the wastewater cycle and prevent pollution?
- Conserve water: Treatment plants remove phosphorus and other pollutants from the water that leaves our homes and businesses, but the plants work less efficiently when sewage is diluted by leaked tap water.
- Learn and Advocate: Learn about your municipality’s wastewater system and advocate for local officials to invest in wastewater infrastructure upgrades. Many communities and local watershed groups work together to disseminate information about how sewage treatment works and what upgrades are being considered.
- Watch a film: Join LCC and partners at a screening of the documentary “Unless Something Goes Terribly Wrong,” followed by a panel discussion on the wastewater infrastructure crisis, as part of the Vermont International Film Festival in Burlington on Thursday, October 22. Ticket information will be available on the festival’s website: vtiff.org.
Lake Look is a monthly natural history column produced by the Lake Champlain Committee (LCC). Formed in 1963, LCC is a bi-state nonprofit that uses science-based advocacy, education, and collaborative action to protect and restore water quality, safeguard natural habitats, foster stewardship, and ensure recreational access. You can join, renew your membership, make a special donation, or volunteer to further our work.