On a recent visit to Chicago, I noticed that Lake Michigan, close to shore, looks more like the waters of the Caribbean (crystal clear, light aqua color). When I grew up in the city years ago the lake was just a bucket of sludge. I’m told the change in clarity is due to zebra mussels ßushed out of the bilges of tankers visiting from Asia. These mussels, I understand, consume the sludge and act like filters, creating the crystal clear waters we see today. Is this true, and will we soon see palm trees on Lake Shore Drive? –Chris, New Hope, Pennsylvania
Best of Chicago voting is live now. Vote for your favorites »
Palm trees, no. There’s this thing in Chicago called winter that the mollusks haven’t been able to do much about. But you heard right–zebra mussels are filtering Lake Michigan’s once-turbid water. The accompanying color change is due to an increase in Cladophora, a type of green algae that thrives on the sunlight that now penetrates farther into the lake’s depths. Before you start planning any scenic snorkeling trips, though, let me tell you the bad news about what’s happening to the lakes.
A zebra mussel is a living water filter, capable of processing about a quart per day. Levels of diatoms–certain single-celled algae–decreased between 82 and 91 percent in Lake Erie after zebra mussels were introduced; the Hudson River saw an 85 percent decrease in plankton after a similar invasion. Lake Michigan, which was formerly cloudy, has been cleared up noticeably by the hardworking little mollusks.
Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.
