From the Vault: Madison in Bloom – Blue-Green Algae Hits Home

A cool, wet Spring and booming populations of algae-munching daphnia couldn’t hold-off the inevitable – Madison’s lakes have been beset by cyanobacteria blooms the last few day. We dusted off this older post to explain what’s going on and precautions you should take during blooms:

The Bloom Begins

(Originally published June 21, 2017) — It was a hot, sunny day and Steve Carpenter couldn’t believe the view from his second-floor office on the shoreline of Lake Mendota. As far out as he could see from his perch in the Hasler Laboratory for Limnology – west to the UW-Madison Rowing team’s boat house and east all the way to the Edgewater Hotel and James Madison Park – the calm, still water looked just like teal-blue paint.

Boaters head up the Yahara River during a blue-green algae bloom. Photo: Katie Rice

It was a massive bloom of toxic blue-green algae and “it is the worst one I’ve seen in a long time,” says Carpenter, director of the UW-Madison’s Center for Limnology. “It’s been many, many years since I’ve seen one this bad.”
In fact, the bloom that hit Madison last Friday, June 16th, was one of the largest blooms to mar Mendota’s shoreline since the summers of 1993 and 1994, he says.
Like this summer, those summers were also marked by “classic” conditions for an algae bloom. Lake Mendota sits in a landscape dominated by agriculture. And some elements of this agriculture, especially the manure produced by dairy operations and synthetic fertilizers used to help corn and soybeans grow, is loaded with phosphorus. This wouldn’t be a huge problem if things would just stay where they’re put.
But this spring and early summer has been marked by not only higher-than-average rainfall (we’re about 35% above normal precipitation levels) but also by intense storm events of 2 inches or more of rain.
All of this rain, especially the “gullywashers,” carry tons of phosphorus-laden soil into nearby creeks and streams, where it eventually ends up in our lakes and is just as good at growing algae as it is soybeans.
Then the weather got warm. 
“So we had perfect conditions for blue greens because they like it warmer than other algae and they grow fast in warm water,” Carpenter says. As soon as it got hot, “we had this incredible spin up of cyanobacteria (blue-green algae) in the lake surface water and then the wind stopped, and these kinds of algae are buoyant and they just floated to the top in this awful scum.”
Fish Kills and Human-Health Hazards
Walleye, panfish and crayfish were just some of the organisms killed in the bloom. Photo: Tyler Tunney

Driven by currents and winds, that scum eventually made its way to Tenney Park, where the Yahara River carries water from Lake Mendota across Madison and into Lake Monona.  By Saturday, the locks at Tenney Park, which allow boaters to move between the two lakes, were sending a frothy cascade of water downstream, adding a white foam to the disturbingly blue-green tint and causing problems far beyond aesthetics.
Fish at the surface, gulping air and trying to escape the bloom. Photo: Tyler Tunney

Tyler Tunney, a post-doctoral researcher at the Center for Limnology, stood on a bridge spanning the narrow waterway and looked down in disbelief. 
“There were dead fish on the surface of the river and others visibly struggling, swimming in erratic circles and literally jumping out of the water,” he recalls. “And it was species like bluegill and other panfish you don’t normally see behaving that way.”
When Tyler went down to investigate he found bodies of fish – from walleye and bluegill to pike and carp – beginning to pile up along the riverbank while crayfish crawled out of the water and died.
He also saw anglers out in their boats nonchalantly casting lines into the water.
According to the Wisconsin Department of Natural Resources, in addition to wildlife impacts, blue-green algae blooms can cause a host of human and pet health problems when they are ingested through swallowing water or come in contact with the skin or, in some cases, are inhaled by boaters or water skiers as they speed through a bloom.
Different species of algae can produce different types of toxins with different types of risks  – some cause inconveniences like skin rashes or diarrhea, others can lead to liver damage, seizures or paralysis.  
Even though Public Health Madison & Dane County has posted signs in advance of Friday’s bloom and despite the news reports of the bloom hitting the airwaves Friday evening, by Saturday morning people were out enjoying their local waterways.
“When the swim advisory signs first popped up along beaches and the UW Memorial Union, people avoided the water,” Tunney says. “Then, by Friday, in the middle of the bloom, people were at out on their paddleboards and, on Saturday, I was watching people fish as fish were literally flailing at the surface of the water.”
The aftermath, dozens of species and thousands of fish killed. Photo: Jake Vander Zanden

To be clear, most algae-induced fish kills occur because of a lack of oxygen, not poisonous toxins. When the huge amounts of algae die and begin to decompose, the microbes doing the decomposing use up a lot of oxygen and produce a lot of carbon dioxide. Eventually fish can’t pull enough oxygen out of the water and try to head to safer waters.
“You would think turbulence of the locks would help [aerate the water],” says Carpenter.
It’s unusual for moving water to get so oxygen depleted that it can’t support fish but, he says, we saw it with our own eyes. “Not only were the fish dying. Crayfish were dying. Other aquatic invertebrates were dying. Basically the Yahara became a dead zone.”
Sign of the Times?
Blue-green stew. CFL professor, Emily Stanley, scooped this sample of the bloom from our pier on Friday. Photo: Emily Stanley

Unfortunately, no one here at the Center for Limnology was taking dissolved oxygen readings in the Yahara River last weekend, so we can’t say exactly how the algae bloom killed the fish. It could also have been toxin or even bacteria-related.
Peter Lisi, another Center for Limnology post-doctoral researcher has been monitoring temperate in the Yahara River and, by Monday, was plotting out his data back in Hasler Lab. Over the weekend, his probes recorded temperatures in the river up near 80 degrees Fahrenheit, the highest they’ve been this year.  While those temperatures alone weren’t causing a fish kill, they certainly aided the warm-water loving algae as it made its way downstream.
“Lake outlets, like the Yahara River, are a reflection of what is happening ‘upstream’ in a lake,” Lisi says. “What happened in Mendota is we had a big bloom and it blew out the outlet and conditions got too harsh for fish.“
Whatever the mechanism behind the fish kills, it’s safe to say that blue-green algae blooms aren’t good for the health of our lakes – or those of us that love them. And there are many parts of this puzzle that are already known.
The primary driver behind algae blooms in our lakes is agricultural runoff. If we’re ever going to fix our phosphorus problem, we’re going to have to start using less of it and help farmers keep more of it on their fields.
“Despite all of the work we’ve done, we’ve still got a tremendous amount of manure on the land and phosphorus in the soil and when we get these unusually high precipitation events, that material can just wash into the lake,” says Carpenter.
Courtesy GLISA

Unfortunately, these “unusually high precipitation events” are getting a lot more common, driven by our warming climate.
And days like last Friday, which hit a recorded high of 86 degrees Fahrenheit, nearly ten degrees over the historical average, will also become more common.
This isn’t “theoretical” or based on “unproven models” as members of Wisconsin’s legislature still routinely claim to the press. Warmer average temperatures have been documented and observed. And more frequent and intense rain events are a reality. We’re already living with climate change.
And, here in Madison, we’re also now living with invasive species like the zebra mussel, which is known to promote blue-green algae growth. 
Take together, all of these changes indicate that, if we can’t get our phosphorus under control, Madison is due for a lot more algae blooms in its future. And a lot more fish kills.
“This is likely not a one off,” says Carpenter. “Particularly if it gets hot again. That was probably just the summer’s first heat wave.”
From aquatic insects to crayfish to fish to this young duckling, the bloom spared very little that was in its path. Photo: Jake Vander Zanden

37 thoughts on “From the Vault: Madison in Bloom – Blue-Green Algae Hits Home”

  1. This is an informative, albeit heartbreaking, article.
    I understand that agricultural runoff is a big part of the equation. I cringe when I see the Tru-Green and various lawn chemical trucks around. Are what they spray all over and what homeowners apply to their lawns also to blame? The lakes ARE Madison. Do we need ordinances or education to help people make better choices in their yards?

    1. Thanks for your comments, Deena. While lawn fertilizer is definitely something we’d rather not have in our lakes, it only accounts for a small percentage of the overall phosphorus “budget.” If we got rid of all urban and lawn runoff but failed to decrease agriculture’s contributions, not much would change in our lakes, I’m afraid. It contributes the lion’s share of the phosphorus.

      1. I think the Limnology department should team up with environmental advocacy groups to support a policy to end this problem. On solution could be the state of Wisconsin could set aside tax money to pay farmers to use less (or no) fertilizer. It would be a cash subsidy in exchange for lower yields, but it would keep our water clean. I’m willing to pay higher taxes for that.

      2. I think the Limnology department should team up with environmental advocacy groups to support a policy to end this problem. One solution could be for the state of Wisconsin to set aside tax money to pay farmers to use less (or no) fertilizer. It would be a cash subsidy in exchange for lower yields, but it would keep our water clean. I’m willing to pay higher taxes for that.

      3. I would like to point out that the lawn care companies are generally better trained than the average homeowner on how much chemical to put on their turf grass — homeowners generally way overdose and it runs off and contributes to the pollution in our lakes. I do agree the major culprit is agriculture. We might increase the county budget in run off control assistance and education.

        1. Hi David, we agree. If we’re going to fix this problem, we’re going to have to help farmers adopt better practices (one’s that generally cost money they don’t have since their margins are often so tight). And as far as lawn care goes, DIY homeowners are definitely more likely to over apply than trained professionals.

        1. Hello! Yes, Wisconsin does have a state-wide ban on phosphorus use as a lawn fertilzer, although its use IS allowed to establish new lawns, or repair lawns, (as well as on sod farms and all agricultural land and production). That said, it’s important to remember that a lawn phosphorus ban only reduces a small fraction of the bigger problem. Lake Mendota didn’t get this green from people feeding their grass!

  2. Everything is related to everything else in the natural world of which we are a part. For many years the Madison community has sought to address excess phosphorus levels in the Lakes by altering one variable, the amount of phosphorus draining from farmland. But climate change-driven weather events and the introduction of invasive species may be altering the equation faster than we can keep up. We need to consider the possibility that even successful efforts to improve conservation farming practices around the Madison Lakes may not prevent further degradation of the water resource or repeated acute bloom events like that of the past week.

    1. We’re not ready to concede defeat just yet! The same climate and invasive species drivers in a northern lake (Trout Lake, for example) won’t produce the same intense blooms and water degredation because that land cover is forest and not ag. Yes, climate change and invasions are making it harder to improve water quality in the lakes. However, several model runs for Yahara 2070 ( show improvements in water quality of Mendota and Monona by 2070. One such scenario is based on extensive technological innovations in agricultural practices, phosphorus management, and phosphorus monitoring. None of these innovations are science fiction; they all exist somewhere in the world today. It is a matter of scaling them up. The second scenario involves massive shifts in land use and management, including a shift away from CAFOs to rotational grazing. Again, these changes are biophysically possible, although political barriers could be significant. The Yahara 2070 model runs include climate changes consistent with state-of-the-art IPCC global models downscaled for Wisconsin. Thus they include changes in precipitation and extreme events that are currently thought to be realistic for our watershed.
      It is important to acknowledge that our water quality problems will not be solved overnight. The whole watershed is eutrophic; the lakes are only the most visible part of a phosphorus-saturated landscape. The residence time of phosphorus in watershed soils is closer to 200 years than to 20 years. We need to keep working to reduce phosphorus and be patient and not give up!

      1. No one’s talking about conceding defeat. But to maintain credibility with the general public, the conservation & scientific communities have to be seen as being on the level. I don’t think that means telling people things may look dicey now, but we have a computer model for when everyone will be 100 years old that is just really exciting.
        My point: the one thing we get when we promise doing conservation better will produce better environmental outcomes is political safety. In this case, we won’t have to tell agriculture that there are way too many cows in the Yahara Lakes watershed, and we won’t have to tell the public that toxic algae blooms are just something everyone will have to live with. I’m pro-conservation right down the line, for all sorts of reasons, but environmental outcomes are what matter. If conservation practices can’t deliver those except in a geologic timeframe, the community needs to be told this, and in plain language.

        1. Sorry! We weren’t suggesting you were conceding defeat, just trying to strike a more upbeat tone! It’s true that legacy phosphorus means we’re committed to some of these outcomes for a long time to come, but even if some of these problems won’t be solved by the time this generation takes their leave, they won’t be solved at all if we never act to correct them. Plus, reducing phosphorus now could indeed reduce the severity and frequency of algal blooms even though Lake Mendota would still be the eutrohpic system we all know and love and are trying to somehow better.

  3. Are there any required shoreline setbacks or barriers between fields, feedlots and water bodies? Should we be building more manure digesters?

    1. In many cases there are vegetated buffers between agricultural activities and surface waters. Unfortunately, buffers can become saturated with phosphorus, and heavy storms can easily overwhelm the buffers and sweep phosphorus into surface waters.
      We should be experimenting with new technologies that keep manure off the land and out of the lakes. Digestors are one potential technology, although the solution is likely to be a lot of different things that include digesters, not only digesters!

  4. Terrific, informative piece. Thanks so much for helping me learn about what happened here last week!

  5. Adam, have you taken a look at any of the USGS studies that have taken place in Madison:
    Pollen in the spring and leaves in the fall are very large sources of phosphorus. The study found that without leaf removal, leaf litter and other organic debris in the fall contributed 56 percent of the annual total phosphorus load in urban stormwater compared to only 16 percent when streets were cleared of leaves prior to a rain event.
    I think it is somewhat unfair to hang the Albatross solely around the necks of farmers. We could also encourage everyone to rake their leaves, bag their lawn clippings, and pick up their animal waste.

    1. Hi Mitch, it is certainly true that urban sources are a contributor to the phosphorus problem. Leaves and grass clippings should be collected or mulched for gardens. Pet waste should be collected. Construction sites should have retention structures to prevent erosion. These practices make a difference, especially in lakes with urban watersheds like Wingra and Monona. Many of these practices have been adopted by municipalities in the Yahara watershed and we are firm believers that any reduction is a good thing and everyone should do their part.
      That said, 80% of the land in the Yahara watershed is currently used for agriculture and ag fertilizer contains a lot more available P than is contained in leaves/pet waste/etc. – so, even if we were to completely eliminate leaves, clippings and pet waste, we wouldn’t have much impact on the amount of P coming into our lakes. We’re not trying to hang an “albatross” around the necks of farmers, we’re just saying that, if we hope to address the problem, our focus needs to be primarily on the primary source of phosphorus. And that comes, for better or worse, from our farmers.

  6. Republicans in the legislature, and Gov. Walker have cut back the DNR, fired scientists and censored information about climate change on the DNR and other state websites. This doesn’t help. They also delayed rules about phosphorous. They are more concerned about businesses than the environment.
    Thank you for the article. It’s sad to know all of these creatures died. But we need to know about it.

  7. As I stood on the shore of the Yahara in Madison last Saturday, it brought to mind the title of Rachel Carson’s book, Silent Spring: toxic-appearing water, dozens of dead fish floating downstream, a sickly duck family too ill to move away from me as I approached. A muskrat sat nearby as well, unmoving and disinterested in its surroundings. It was the most alarming thing I’ve seen in quite a while.

  8. Is there any information on how much and for how long these nutrients are likely to stay in the system? Example, are these nutrients being sequestered in sediments that could later be stirred up?

    1. Hi JDT, yes, phosphorus is absolutely being sequestered in sediments. Some estimates say that our soils are so super-saturated with phosphorus that, even if we stopped using it altogether, they’d be releasing some P into our waters for 100 years. That said, the algae bloom this article is about wasn’t from “legacy” phosphorus but from phosphorus that washed into the lake this spring, so reducing P loading will have positive impacts, even if we’re waiting for legacy P to clear out of the system.

  9. I haven’t read all the posts and maybe I am just repeating somthing that someone else has suggested, but what about building UP the shoreline around them to prevent the runoff? Sounds like a solution to me.

  10. Solid particles like organic matter, silt, and clay contain only 30% of the phosphorous coming into the Lake Mendota. 70% is soluble phosphorous. Therefore, we must keep the runoff water out of the lake, not simply the solid particles, and this is a much more difficult proposition.

    1. Hi James, the actual percentages are a little more like 50/50. For example,dissolved inorganic P constituted 51% of total P on both of the USGS long-term inflow monitoring stations to Lake Mendota during 5 recent years. So about half is tied up on our top soil and half dissolved in our water. But your larger point is spot-on, it’s near impossible to just keep water out of our lakes, and is a much harder P source to control than sediment-associated P that can be controlled by typical farm conservation practices. It would be difficult to keep runoff water from coming into the lake, so what we need is to spread far less raw manure (and P commercial fertilizers) on agriculture fields as a way to reduce soil P levels and hence to reduce dissolved P concentrations in runoff water.

      1. Since this type of blue-green algae bloom is likely to happen any time we have excessive rainfall in Dane county, we need an inexpensive solution to the big Yahara river fish kill.
        How about installing a 3 to 4 foot diameter pipe out into the lake to a depth of 15 to 20 feet, and connected to the Tenney locks outlet to the river, with a valve that can shut off the normal surface water flow and replace it with clean water from deep below the surface?
        My guess is this would not cost more than $200,000, since the underwater piping could just be galvanized steel culvert.

        1. Hi Kevin,
          Unfortunately, the pipe idea may not achieve the desired results. The deep water of Lake Mendota is far from “clean” – many of the nutrients in question eventually precipitate out to the bottom water and, by mid-summer, when the lake is stratified (meaning the warm, surface water doesn’t mix with the cold, bottom water) that cold, bottom water also has no oxygen.

    1. Hi Brent,
      Citizens can absolutely do their part to limit their contributions of phosphorus to the lake – rake up your leaves, don’t use lawn fertilizer, etc. – but since the majority of phosphorus comes from agricultural runoff, there’s not much to be done other than support policies and organizations that help farmers install best management practices in dealing with runoff and reducing the amount of P they put on the land in the first place.

  11. This type of article is absolutely infuriating. Necessary information, I guess, but infuriating. It appears that there’s essentially nothing we urbanites can do that will substantially alleviate the problem, our politicians aren’t listening/not interested/not acting, and our farmers won’t or can’t afford to change their practices. To top it off, even if the runoff problem was solved today, the lakes will be disgusting cesspools and wildlife deadzones for another generation. Thoroughly discouraging…

    1. Hi Ken, we understand your anger, but don’t lose all hope! While there are some deadzones and the lakes are sometimes unswimmable, there is a LOT of life left in them yet and they sure can be nice places to be! The article was a response to very paltry and incomplete news media coverage and, honestly, to the fact that urban, residential and agricultural sources of P are often reported on as equal contributors to the problem, when that isn’t the case. Still, take heart. While there may not be widespread political action on this, Dane County, Madison Metropolitan Sewerage District, area farmers and countless non-profit organizations ARE making progress. Unfortunately, thanks to increased precipitation, warmer days and intense storm events all likely associated with climate change, the positive impact current phosphorus reduction efforts are having is being obscured. I know it’s not very heartening to hear that “it could be worse,” but it would, indeed, be much worse without current efforts. If we continue these efforts and get the lion’s share of focus on agricultural runoff, we will indeed see positive change. It’ll take time and effort, but it’ll happen!

  12. Has there been anyone looking at using enhanced biological phosphorous removal to reduce the levels in the lakes? I’m not sure what the minimum size of the process needs to be but it seems like at least getting something working as a proof of concept could be helpful. Especially if it could be designed to be distributed to cover the main inflows to the lakes.

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