It’s Spring 2016! Help Us Monitor Mendota’s Clear-Water Phase

Last year at this time, we asked you to help us monitor Lake Mendota, as we worried that we’d missed its “clear-water” window. We’re happy to report that, in 2016, we’re nearing a 6 meter Secchi depth and seeing lots of daphnia in our nets. Will this be a clear spring for Madison’s lakes? Stay tuned. Until then, enjoy this post from last year! And feel free to help us #MonitorMendota!


by Jake Walsh, May 20, 2015

Spiny water flea under the microscope. Photo: Jake Walsh
Spiny water flea under the microscope. Photo: Jake Walsh

We’ve written before about how an invasive zooplankton called Bythotrephes longimanus, or “the spiny water flea” (SWF) is eating our native algae-grazing friends, the tiny crustaceans called Daphnia.
This is important because, as phosphorus pollution leads to algae blooms and lower water quality, we are also losing the critters that keep that algae at bay and give us our annual spring “clear-water” phase. 
Since SWF was first detected by a group of UW-Madison undergrads in Lake Mendota in 2009, we’ve lost over 80% of our Daphnia pulicaria (the big Daphnia that eat a ton of algae) and over 2 feet of water clarity in Lake Mendota.
Image: Jake Walsh
Daphnia abundance and Secchi depth before and after spiny water flea detected in Lake Mendota. Image: Jake Walsh

However, 2014 may have been the worst yet. The intensity of SWF predation on Daphnia in the fall of 2014 was twice as high as any other year we’ve observed. It was so bad that, on September 2nd of 2014, the voracious spiny water flea caused the collapse of Lake Mendota’s Daphnia community and they still haven’t recovered as of today.  Where I used to pull in hundreds of thousands of Daphnia pulicaria in a single sample, I’m now often only finding a single tiny individual in my net.
If you love clear water, then these little Daphnia pulicaria are your best friend! Are we losing them in Lake Mendota?
If you love clear water, then these little Daphnia pulicaria are your best friend! Are we losing them in Lake Mendota?

While we’ve seen “tough times” for Daphnia before, we’ve never witnessed anything like this in the four decades the Center for Limnology and Long-Term Ecological Research (LTER) scientists have monitored Lake Mendota.
As a result, water clarity in Lake Mendota has been downright dismal this year while Lake Monona, which doesn’t have a large SWF population, is looking nice and clear. In fact, last year’s average water clarity was BETTER in Monona than Mendota for the first time since we’ve been keeping records.
Lake Monona is in it's spring clear-water phase - is Mendota close behind, or out of luck? Photo: Hilary Dugan
View straight to the bottom – Lake Monona is in it’s spring clear-water phase – is Mendota close behind, or out of luck? Photo: Hilary Dugan

So – we’re asking for your help. We’d love to hear from you about what you see on Lake Mendota.

If you’re walking by the lake, boating on the lake, hanging out at the Terrace, relaxing on a pier – wherever you are, we’d love to hear about what you’re seeing this spring. If you want to call yourself a “citizen scientist” go for it – all we’re asking is for you too keep your eyes open and report back about what you’re seeing.
Here are some things you might keep track of on your next trip to Lake Mendota or ANY Madison lake:
If you have a Secchi disk, then you know the drill (or if not, check out How To Use a Secchi) and send in the date, time and location of your Secchi depth reading.
If you don’t have a Secchi disk, no worries – we have a cool-water challenge for you:

  • Walk into the lake until you can’t see your feet. (Please stop walking if you get to your chest and can still see your feet!)
  • Where were you wading? When? How deep is the water at the point that you can no longer see your feet? Knee height? Ankle? Thigh? If you’ve got a tape measure or yard stick, send in your reading (we’ll convert to meters!)

If you’re feeling industrious – Make your own Secchi Disk:

Take and post plenty of pictures!  Send them to or post them on our “Center for Limnology” Facebook page or tag @WiscLimnology on Twitter and use the hashtag – #monitormendota

In the meantime, I’ll be providing weekly updates of my own sampling trips and how our stressed Daphnia community is doing at bringing in the clear water phase. Please help us keep a watch on our lake and, hopefully, we’ll all get to celebrate the arrival of this year’s clear water phase!

Where's our clear water? Lake Mendota. May 8th. Maybe 10 inch Secchi depth. Photo: Jake Walsh
Where’s our clear water? Lake Mendota. May 8th. 10 inch Secchi depth. Photo: Jake Walsh

Post Script:
Last week (May 8th) I  found a single Daphnia in a net tow where I towed through as much water as could fill a Mini Cooper (~70 cubic feet; we typically find tens or hundreds of thousands) and a Secchi depth of only 1.6 feet. That’s almost 17 feet lower than what we would expect this time of year before the SWF arrived and over 9 feet lower than what we’ve come to expect since the SWF arrived.
To put 1.6 feet in perspective: the wake of my boat looked like the chocolate river in Willy Wonka’s chocolate factory (diatoms, a type of algae, make the water look brown).

12 thoughts on “It’s Spring 2016! Help Us Monitor Mendota’s Clear-Water Phase”

  1. Hi Jake! Please let us know how Clean Lakes Alliance can help! We have over 45 volunteer monitors out on the lakes this summer, and lifeguards at the City of Madison beaches. We’d love to coordinate with you to get you more information from more sites. Please be in touch!

    1. I’ve been wondering why the water in front of my house (in Gov Nelson State Park) looks so awful this year. There hasn’t been a single day when I can see the bottom (32″ at the end of my pier) that went in May 1. The water is brown and splotchy.

      1. Hi Jacob,
        The brown water is often the result of diatoms, a unicellular kind of algae that is a favored food of daphnia. So, when daphnia populations are low, you’ll often first see diatoms taking advantage of low predation pressure.

  2. I have been monitoring lake Waubesa as part of the citizen monitoring program through clean lakes alliance. Waubesa has been quite clear 120+++ on the turbidity tube this year. . I did capture some daphnia earlier(I think)..they were quite abundant. I would love to know how to stem the tide of the swf. Waubesa would be a good place for monitoring as the daphnia are not yet decimated.

Leave a Reply

Your email address will not be published. Required fields are marked *