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What summer flooding means for Lake Champlain water quality and cyanobacteria blooms

A photo from above of brown water leaching into dark blue water around land forms.
Vermont Online Library
Floodwaters flow into Lake Champlain in Milton on July 11, 2023.

Recent heavy rains have led to phosphorus runoff and sewage leaks into Vermont lakes and ponds. Cyanobacteria blooms have closed beaches along Lake Champlain multiple times this summer, with warmer water temperatures due to climate change causing the blooms to occur more frequently.

Even if the lake looks safe to the eye for a swim, it might not be.

Vermont Edition host Mikaela Lefrak spoke with Jeffrey Schloss, the acting extension program leader with the Lake Champlain Sea Grant, an organization which develops and shares scientific knowledge to benefit the Lake Champlain basin. A portion of their conversation is below, and has been edited and condensed for clarity.

Mikaela Lefrak: Now, Jeff, when you saw the flooding begin in that second week of July, I'm curious what your first thoughts were as somebody who has monitored water quality in this region for years?

Jeffrey Schloss: We know that when we have floods of that magnitude, we tend to see a tremendous amount of movement of materials into Lake Champlain and all the other lakes around Vermont, because of the higher velocity of water and the capability to essentially carry more suspended materials... And so we know that events like that could actually represent close to 80 to 90% of the year's loading of nutrients, for example, coming into lakes that are receiving those waters.

So when you when you saw this flooding happen ... as you're thinking about what what was to come for Lake Champlain, that must have been a must have been a very difficult moment.

Well, of course, the real concern was for the flooded communities, and the economic impacts, and the changes to habitat. So that was really my primary concern. But of course, secondarily, we're very interested in what the impacts will be on the lake water quality. We saw for a time after and even continuing now, we have new loads of sediment in the deltas where the rivers come into the lake, where the tributary rivers come in.

We also saw from remote sensing, as well as satellite remote sensing as well as our own UVM drone sensing, we saw the tremendous amount of sediments that not only you could see in the in the in the rivers as they were coming into the lake, but you can see in the lake. So there was a tremendous amount of sediment load and of course attached to that sediment, all sorts of nutrients and potential pesticides and other types of pollutants that were delivered to the lake.

I believe I saw some of that drone footage. And it's pretty remarkable how visual it is — that you can really see the sediment flowing right into the lake.

Yeah, and some of our areas have a lot of very fine clays, which mean that that sediment will stay up in the water column for a very long time before it settles down, since it's such fine material. Some of the heavier materials that are moved essentially just fall right as they enter the lake and create those deltas because they're heavier and the velocity slows down when the river water enters the lake. But those clay particles will be there for a long time.

Now, Jeff, I read that state officials said that over the course of a week in July, 130% of the entire phosphorus load from 2022 for the Lamoille River flowed into Lake Champlain. And there was also a lot of runoff coming from the Missisquoi River as well. Talk us through what that means. That sounds like an enormous increase.

Yes, that is, and the fact that we still have some summer to go, it'll be interesting to see how the lake reacts. You know, the lake is essentially going to be the reaction vessel where all of that material has now come in. And any of the available nutrients will definitely be worked on by all the various organisms in the lake, and we will be really concerned to see whether or not that will result in in seeing bloom activity occur, depending upon how high the the water remains, as well as how calm we have in terms of the coming weather as we approach the fall.

A photo of green substance on the blue surface of water.
Elodie Reed
Vermont Public File
A cyanobacteria bloom is pictured on Lake Champlain in St. Albans in August 2019.

Well, let's talk about those blooms, the cyanobacteria blooms, specifically. Those close down beaches, they affect the ecosystem. What is cyanobacteria? What is a cyanobacteria bloom?

Essentially, cyanobacteria are some of the most primitive bacteria, photosynthetic organisms we've had on Earth. In fact, most people attribute the oxygen in our atmosphere that was created to them, since they were the earliest sort of synthetic organisms.

They're one of many types of bacteria that are photosynthetic that you can find in waters. They're found all over the place in the oceans and in our waters. Typically they don't become problematic until there's a combination of very warm water as well as a lot of excess nutrients which then drive them to outcompete all the other photosynthetic algae in the water. And, what we then will see is a bloom, sometimes we see blooms because there's just so much productivity occurring, because of the nutrients. Sometimes we see blooms because there are there are smaller amounts of the bacteria that are growing, but then the the wind will push them in, in towards shore into bays and embayments. And so they will collect.

They tend to be distributed early on in the bottom waters and sometimes mid-lake depths. And towards the end of the season, we tend to see them come up into the upper area of the water column and collect. You'll definitely see them as greenish, or blue-greenish blooms that sometimes look like small little pin-size balls or, or sometimes looks like spilled paint.

There are other types of algae that do bloom, but they tend to be look more stringer and, as opposed to more shinier, or flakier or more kind of bubbly. So they're generally very visual when you see them. And that's when we become most concerned about their accumulation, because they do produce a number of toxins on occasion. Those toxins are either neurotoxins or liver toxins, they also produce other irritants. And there's some people that will react to them by having rashes occur when they come in contact with them.

So there are a lot concerned about those toxins, because there are some very acute situations where even if we have small children or small pets drinking water with a bloom with toxins in them, we could see tremendous problems. Dogs have been known to die from drinking lake water. And kids can get very sick.

So we're very concerned about about when they accumulate and produce toxins. And again, there are these short term exposure concerns. But we also have some long-term concerns, because we see that long-term exposure has the possibility of causing certain neurological diseases and disorders.

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OK. So there's the cyanobacteria blooms caused in part by the increase in phosphorus runoff. And then in mid-July, there was a sewer pipe that ran under the Winooski River that brokeand at its height, it was spewing 350,000 gallons of wastewater into the Winooski, which feeds into Lake Champlain. That's about 10% of Burlington's total sewage flow. What kind of setback to clean up efforts does a break like that pose?

Well, of course, you have the instantaneous concern from the other type of bacteria that we generally post warnings on beaches [about], the fecal coliform bacteria, which are indicators that if we have the presence of sewage coming into the water, especially if people are using it to recreate. There's a very high chance of other pathogenic organisms to be in the water — those organisms, bacteria and viruses that cause disease parasites. So that's the main number one concern right away.

Secondarily, of course, you have this large amount of nutrients — wastewater contains a tremendous amount of of phosphorus and nitrogen — untreated wastewater. So we had that concern of additional nutrients coming into the lake besides what was brought in from the sediments and in the runoff from the stormwater and the flooding events.

So hearing about that sewage break, did that just make you want to scream?

Well, you know, it's very unfortunate that that happens, it was very good that they contained it, as soon as they can. We do have situations in a number of areas around the lake where we still have combined sewer and stormwater systems that overload the the wastewater treatment plants. And essentially, we do have situations during very heavy storms then, that even without a pipe break, we do get combined stormwater runoff with with some septic.

So we see that occurring. But the fact that they were able to repair it fast was very helpful. But we will be looking to see what the what the outcome is in terms of that nutrient loading in terms of the lake response.

Now, Jeff, I was down in North Beach on Lake Champlain over the weekend, and there were lots of folks swimming in the water and enjoying themselves. But I've also had conversations with folks who say, "You know, after the flooding in July, after the the sewer line break, I don't want to get in the water right now." So what's your guidance for folks on how to know when it is safe to swim?

Well, there is a cyanobacteria tracker, that takes data from volunteers that work all around the lake that take water samples very often. And I was taking a look at those results just for over the weekend, for example. And even earlier this week, there are some actually from yesterday that aren't showing any heavy blooms — except for areas around St. Albans in that northern part of the lake, which which tends to be problematic all the time.

So in terms of cyanobacteria, and they typically also test the beaches themselves — are tested for coliform bacteria to make sure that there wasn't any flow.

Because it was relatively dry for a while, generally the ultraviolet sunlight will take care of a lot of pathogenic organisms at the surface in shallow waters. And when we do have rain events that don't bring in a whole mess of material, because they're short-term events that don't cause flooding, we do get at least some flushing of the base and embayments, so that we kind of wash out the cyanobacteria and dilute the other potential problematic organisms in there, and we get the lake flowing.

It's really when we have the really quiet times and very hot weather, especially in the shallows and the embayments, or winds that are blowing from the the middle of the lake towards towards shore that we then tend to be concerned about the accumulation of cyanobacteria.

So, you know, in general, you can never guarantee what the condition of the water is at any time. Even after it's just been monitored, because everything's moving about and everything's dynamic. But if you don't see a bloom, you shouldn't necessarily be that concerned about cyanobacteria. Because typically — as I said, even some of the blooms don't produce toxins — but we've never measured toxins where we didn't have a boom.

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Mikaela Lefrak is the host and senior producer of Vermont Edition. Her stories have aired nationally on Morning Edition, All Things Considered, Weekend Edition, Marketplace, The World and Here & Now. A seasoned local reporter, Mikaela has won two regional Edward R. Murrow awards and a Public Media Journalists Association award for her work.
Andrea Laurion joined Vermont Public as a news producer for Vermont Edition in December 2022. She is a native of Pittsburgh, Pa., and a graduate of the Salt Institute for Documentary Studies in Portland, Maine. Before getting into audio, Andrea worked as an obituary writer, a lunch lady, a wedding photographer assistant, a children’s birthday party hostess, a haunted house actor, and an admin assistant many times over.