UVM researchers monitored St. Albans and Missisquoi Bays of Lake Champlain in summer 2021 and found Missisquoi had substantially higher cyanobacteria mass and, in some cases, up to double the nitrogen of St. Albans. The study suggests nitrogen — from vehicle emissions, agricultural and industrial runoff and intensified by storms — can fuel blooms alongside phosphorus. Scientists warn storm-driven nitrogen pulses can quickly alter lake ecology, and that total algae counts don’t indicate toxicity. Further research will clarify which blooms are harmful and how best to manage nitrogen inputs.
New Study: Nitrogen — Not Just Phosphorus — Is Driving Algae Blooms in Vermont's Lake Champlain
UVM researchers monitored St. Albans and Missisquoi Bays of Lake Champlain in summer 2021 and found Missisquoi had substantially higher cyanobacteria mass and, in some cases, up to double the nitrogen of St. Albans. The study suggests nitrogen — from vehicle emissions, agricultural and industrial runoff and intensified by storms — can fuel blooms alongside phosphorus. Scientists warn storm-driven nitrogen pulses can quickly alter lake ecology, and that total algae counts don’t indicate toxicity. Further research will clarify which blooms are harmful and how best to manage nitrogen inputs.
06:07 AM, 11/18/2025Environment
Why algae blooms are rising in Vermont lakes
BURLINGTON, Vt. — On the hottest days, swimmers at Lake Champlain and other regional lakes often find beaches closed due to algae blooms. A new study from the University of Vermont (UVM) shows that nitrogen — alongside phosphorus — can be a key driver of those blooms.
Study findings from summer 2021
UVM researchers monitored St. Albans and Missisquoi Bays throughout the summer of 2021 and found that Missisquoi Bay contained a substantially greater mass of cyanobacteria and, in some cases, up to double the nitrogen concentrations measured in St. Albans Bay.
“We don’t pay as much attention to nitrogen as we need to,” says Ana "Mindy" Morales, a limnologist at UVM.
“We saw nitrogen in Missisquoi Bay being in some cases double of what was in St. Albans Bay,” says Katelynn Warner, lead author of the study and a former UVM doctoral student.
Where the nitrogen comes from
The U.S. Environmental Protection Agency notes nitrogen enters waterways from multiple sources: vehicle emissions that produce nitrogen oxides, runoff from agricultural fields and livestock operations, and industrial discharges. Heavy rains, floods and storm events can mobilize and concentrate these nutrients, sending pulses of nitrogen into lakes that may trigger or intensify blooms.
What this means for health and management
Not all algal blooms are toxic; measuring total algal biomass does not determine whether a bloom poses a health risk. The researchers recommend broadening water-quality strategies to address nitrogen as well as phosphorus. Warner plans to return to UVM to investigate which blooms are toxic and to better understand how weather-driven nutrient pulses affect lake ecology.
ABC22/FOX44 also interviewed environmental health scientist Bridget O’Brien earlier this summer about how weather can influence algal blooms.