Every so often cities such as Chicago, Evanston, and Wilmette will close down their beaches due to higher than normal bacterial counts. Have you ever wondered why that happens?
In this podcast, we speak with Todd Connor who is a candidate for Commissioner for the Metropolitan Water Reclamation District of Greater Chicago. Be sure to listen in as we talk about the history of the district, how it operates, and why we should be concerned about who’s watching over Lake Michigan.
Many of us recall our grandparents warning us about “undertows” or “undercurrents” along the coastlines of the Great Lakes or the oceans. A bit later on, the term “rip tides” came into vogue only to be replaced by the contemporary version of “rip currents.”
There’s been a lot of buzz over the past few days about how cold the lake has become in such a short period of time. Dave was out swimming earlier today, and he left me a voice mail message proclaiming that it was the coldest August swim he has ever experienced in 34 years out at the lakefront. With that in mind, I felt compelled to get an empirical measurement from the field…
I took a quick jog down to Ladder #1 and jumped in with just my goggles and swim shorts. And let me tell you something – the rumors are true.
There is a layer of temperate water on the surface that is anywhere from six inches to three feet deep, depending on where you are swimming. This is the pleasant 65F+ water we’ve been enjoying over the past month. Below that, all bets are off. It’s 55F. Tops. Probably even colder as you get below the three foot level.
I’m fairly certain this is just the colder thermocline layer mixing it up with the warmer top layer. But the water seems unusually cold, more reminiscent of October. There is a possibility (although very slight) that the lower-than-average temperatures we’ve been having this summer coupled with the windier days have pushed up the fall turnover by six weeks or so.
Let’s pray to the water deities that this is NOT the case!
Besides Ladder #1 itself, one of the more iconic items out at the swim site is that peculiar structure that looms way out on the horizon. You see it showing up in many of the photos we take. In fact, you can see it on the banner at the top of the website.
That structure is the Harrison-Dever Intake Crib, and it’s actually composed of two interconnected buildings.
The older of these two structures is the Carter Harrison Crib which was built in 1900 and named after the Chicago mayor at the time.
The William E. Dever Crib, also named for a former Chicago mayor, was completed in 1935 to replace the Carter Harrison crib (however, an increased demand for water kept the Carter Harrison Crib fully operational until 1997).
These days, the Harrison-Dever Intake Crib provides water to the city of Chicago by pumping it through a 20 foot diameter tunnel that runs underneath the lake and connects the water crib complex to the James W. Jardine Water Purification Plant, located just north of Chicago’s Navy Pier.
A lot of Chicagoans still refer to the Harrison-Dever Intake Crib as the “Two-Mile Crib” for a couple of reasons. The more obvious one is that it is indeed located two miles off of the Chicago lake shore. However, the historical reason is that the Carter Harrison Crib replaced an even older structure called “Two-Mile Crib” which was originally constructed in 1865.
The Two-Mile Crib was connected to a tunnel built 60 feet below the lake surface, and this tunnel ran all the way back to the Chicago Avenue pumping station – which was part of the historical Water Tower complex still located today on north Michigan Avenue.
Right now, there is a thin layer of water on the surface of Lake Michigan that is colder than 39F (4C) and therefore less dense. This thin layer of water floats on top of the lake and under the ice throughout the winter. We’ve been swimming in this less dense layer of water since November.
However, were we to dive down past 30 feet, we would find the lake temperatures increasing to 39F and remaining at that temperature all the way to the bottom of the lake. This layer is known as the hypolimnion, which is a constant in cold, deep-water lakes. So over the past few months, we’ve had this scenario:
With the arrival of spring, the ice melts off of Lake Michigan and the top layer of water on the lake gets warmed by the increasing levels of sunlight. Once the surface temperature reaches 39F, the surface waters sink until the water temperature at all depths reaches approximately 39F. This sinking, combined with spring winds mixing up the water, causes a phenomenon known as the “spring turnover” which is beginning to take place right now:
As spring transitions into summer, warmer water collects on the surface and the lake eventually stabilizes into three layers:
As the summer wanes into fall, the surface temperatures cool and the process reverses itself. We get a similar turnover in the fall, and then we’re back in winter mode.
The key point to note here is that the majority of Lake Michigan never really goes above or below 39F. In addition, due to its enormous variability in surface area and depth, Lake Michigan is never really that far from lapsing back into “turnover mode” on both ends of the summer months.
So always be sure to bring a variety of gear with you out to Ladder #1, because you never know what you might get – even in the middle of the summer!
On September 16, 1967, Chicagoan Ted Erikson swam from the Farallon Islands to the Golden Gate Bridge. The 31.5 mile swim took Ted 14 hours and 38 minutes to complete:
What’s particularly amazing about this feat is not the distance – other record holding swimmers have done much greater lengths. And it’s not the 50F-60F temperatures – other intrepid souls have braved much colder water.
It’s what was in the water:
Whenever you find yourself hesitant to venture out to one of our earlier swim meetups, I want you to revisit Ted’s video and keep a few things in mind:
- You will be wearing a wetsuit
- You will not be swimming for 14+ hours
- You will be finished with your swim long before it gets dark
- You will not be swimming in the open ocean, completely vulnerable, in an area chock full of predatory fish the size of (no exaggeration) a Chevy Suburban.
Date: Sunday, April 20, 2008 Time: 6:00AM Location: “Chessboard” area about 600 meters north of Oak Street Beach Swim plan: 10-20 minutes of low exertion swimming depending upon the temperature/weather Notes: We’re way early in the season, but I thought I’d throw out a tentative date for our first meetup. I won’t candy coat it for you – the water will probably be very “brisk” to say the least. I’m expecting 50F – 55F (10C – 12.5C), which is pretty much the lower limit for what I consider to be safe swimming. I’ve seen some brave souls swim in this temperature range without a wetsuit, but I’m certainly not one of them. So I’d recommend you pack the following:
- Cold water gear (wetsuit, booties, neoprene cap, neoprene gloves, thermo shirt, petroleum jelly)
- Towel
- Post swim warm-up clothes
- Bike lock
- Hot tea or coffee
Stay tuned for further updates as we get closer to the date.
