When we moved to Cleveland in 2014 and I saw Lake Erie up close, one of the things that took me by surprise was the color of the water. Standing on shore and looking out in the summer months, in many places the most visible stretch of water has a gorgeous blue color – it can be close to a turquoise. I’ve now seen this color in Lake Michigan, and memorably in Lake Superior, as well.

The color of Great Lakes waters varies tremendously of course – season to season, day to day, even hour to hour depending on weather and lake conditions. It can have a steel color, a deep green-brown, a dark blue.

But the turquoise, gem-like blue is something that many people notice and comment on – usually with enthusiastic disbelief.  People who grew up on the shores of the Great Lakes in past decades describe returning to one now and finding clear water in remarkable shades of blue. 

People flying cross-country might even notice it from an airplane. A cousin of mine flying between the west coast and New York City described looking out the plane window and being completely disoriented.  “We didn’t know where we were!  It didn’t make sense that we were above the Carribbean!”

I’ve been reluctant to share with people what I have learned about that bright turquoise blue.  Unfortunately, this striking color and clarity is not a sign of lake health as we would be inclined to think.  Instead, as Dan Egan writes in The Death and Life of the Great Lakes, it’s a sign that “the life is being literally sucked out of the lakes”.

A write-up from a 2019 segment on Chicago’s WGN 9 TV station summarizes a number of key points.

Many people think that water appears blue due to the sky. There is an element of light and refraction that can impact the appearance of a body of water. But it’s also the case that water radiates blue.

Water color is impacted by things in the water. Algae, decaying material and sediment can all be churned up in the water causing a color to shift. 

It’s also impacted by things not in the water. In the case of the Great Lakes, it’s the absence of healthy algae that used to be omnipresent in the water that has lightened or made many of the lakes “more blue”. The criminals in this storyline are the zebra and quagga mussels that arrived in the lakes sometime around the late 1980s and have since spread relatively uncontested. In a stunning statistic, scientists say there are so many mussels in Lake Michigan that they can filter the entire volume of the lake in four to six days, and they have reduced the amount of light-absorbing algae by over 50%.

So now when I look down into the lake and see clear waters and white sandy bottoms, I feel a tug of mixed emotions: a socialized response of what is thought to be beautiful waterscape and an ecologist’s gut feeling that all is not as it should be.