A year after historic flooding wreaked havoc across Vermont, extreme rain once again supercharged rivers across the state in mid-July. All that water picked up sediment, garbage and chemicals.
Vermont Public's climate reporter Abagael Giles joined Mary Williams Engisch to discuss Vermont's water quality post-flooding. This interview was produced for the ear. We’ve provided a transcript below, which has been edited for length and clarity.
Mary Williams Engisch: Can you give us the big picture: How does this year’s flooding compare to last year's?
Abagael Giles: Yeah, it was kind of two years in a row of these weather patterns that have happened in Vermont in the past, but are more intense now because of human-caused climate change.
But one key difference is last year we saw more widespread extreme rainfall — a few storm systems kind of got stuck over us. This year, the rain was more intense in some places, but generally shorter-lived — though it was very destructive for humans.
All that means that in the grand scheme, scientists are saying they expect the water quality impacts of this year’s flood to be less significant than last year.
Data from the Department of Environmental Conservation already show that:
- In 2023, 28 wastewater treatment facilities broke down because of flooding or high flows, leading to raw sewage spills. This year — in 2024 — just nine did.
- In 2023, north of 6 million gallons of untreated sewage spilled into Vermont waterways, with more if you include combined sewer overflows. The state says the 2023 figure is an underestimate because they’ve since improved their reporting system.
- In 2024, just over 40,000 gallons of untreated sewage spilled into Vermont waterways, but we saw more than 14 million gallons in combined sewer overflows.
So, still bad, but not as bad.
Mary Williams Engisch: Abagael, I take it that flooding is not good for clean water.
Abagael Giles: Yeah, extreme rain turns our rivers into big spigots. You see these high velocity flows, and all this stuff gets washed away.
Fuel tanks can spill, cleaning supplies, industrial waste, wastewater systems get overwhelmed or flooded, you can have raw sewage in the water — but also, nutrients like phosphorus and nitrogen, which in high amounts can be bad for lakes downstream and lead to more cyanobacteria blooms.
Forests and wetlands can really help pull this stuff out of rainwater before it hits the rivers or lakes, but ultimately, what goes into a river winds up in a lake or in the ocean.
And all this water rushing through our rivers is a natural phenomenon — it’s not bad on its own. The water system is supposed to work this way. But what’s different now is that us humans have put a lot of unnatural stuff in places where it gets carried away.
Mary Williams Engisch: You had a chance to get out into Lake Champlain with some scientists and actually look at the impacts yourself. What did you see?
Abagael Giles: Yeah, I went out on this research vessel with the Lake Champlain Sea Grant Program. It’s kind of like a floating laboratory for keeping tabs on how clean the lake is.
We left from Burlington Harbor and went up to the mouth of the Winooski River, where you could see this plume of brown water that went almost to the middle of the lake.
Matthew Vaughan: This is mostly from the Winooski River, which is really just running very turbid right now, meaning there’s a lot of sediment that’s suspended in the water.
Abagael Giles: That's Matthew Vaughan, the chief scientist with the Lake Champlain Basin Program. He says last year’s flooding dumped half of the phosphorus Lake Champlain is supposed to get in a year into the lake in one week.
It was a record-setter. They don’t expect the dump from this latest flood to be another one, but there are still big impacts, and you may have noticed at your local swimming spot.
Matthew Vaughan: Whenever we have an intense rainstorm, bacteria can wash into the lake and kind of elevate those bacteria counts for a usually short period of time.
Abagael Giles: Vaughan says that this particular issue should mostly be cleared up by now, but it’s a good idea to check to see if your local beach is open for a few weeks here.
Long term, all those nutrients kind of act like food for cyanobacteria, or blue-green algae blooms.
[The scientists] actually dropped a little disk into the water in the plume and outside of it, to measure just how cloudy the water was.
And there was a big difference. But Vaughan and the other scientists on the boat say flooding is a normal and healthy part of Lake Champlain’s history.
The problem is, most of the flooding used to happen in the spring. And now, because of climate change, it’s happening in the summer, and more often.
Matthew Vaughan: And it’s part of a larger trend of more intense, more frequent rain storms causing more flooding. And also a shift in timing of when we’re seeing water and nutrients and pollutants enter the lake.
Abagael Giles: And that’s working against Vermont’s efforts to reduce those nutrients by conserving wetlands and forests, and changing the way people farm. It could be leading to more toxic cyanobacteria blooms.
Mary Williams Engisch: It's so interesting, that big plume you're describing. I want to ask a bit more about climate change. Do scientists think our rivers can keep up with all this happening so often?
Abagael Giles: It’s a great question, Mary. And honestly? The ones I talked to at University of Vermont, the Lake Champlain Basin Program and the state? They’re worried.
We talked about nutrient loading, but no one is really keeping tabs right now on what happens to all the chemical contaminants that get swept downstream in a flood.
UVM is working on some new research into microplastics in the lake.
But, you know, scientists, they want to be clear: When it comes to phosphorus and nitrogen and all the dirt that floods carry, rivers and lakes are dynamic. Flooding has always been a part of this place, and the lake does recover.
But in the more distant past, we had more wetlands and older forests to scrub all these nutrients out. Plus, our rivers weren’t straightened and dredged.
And scientists also told me: This trend of more frequent flooding, with heavy flows in the summer, is a big change for the ecosystem. It could threaten some of those big investments — in taxpayer dollars and changes to industry — that Vermont has made, and that Vermont farms have made, to reduce how much phosphorus and nitrogen get into the lake.
So yeah, they’re wondering, "Do we need new policies to try to keep up with our changing climate?" And, "Are our current clean water regulations up to the task?" I think there’s a lot we still don’t know.
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