With the size of the Great Lakes, it wouldn't be that surprising that some bays or inlets would be clean while others were disgusting.

I don't know about Lake Michigan, but I wouldn't really have advocated swimming in the parts of Lake Ontario I was around in the '80s.

I was living in Toronto in the 1990's and I wouldn't swim in Lake Ontario if you paid me.

And anyway this is a seasonal effect brought on by a larger than usual ice content this past winter. If I read the article correctly this won't last long and run off from surrounding farms and industry will have the lake algae ridden and opaque before too long...

I wouldn't be so quick to blaim run off without evidence that this is the main cause. Diving in the ocean in northern Europe you experience the same thing: you have a choice between 4 degrees C and clear water or 15 degrees C and murky green. Runoff isn't a significant cause of plankton blooming in the North Atlantic. Temperature is.

Still, it requires nitrogen to get an algae bloom, right? Has to come from somewhere.

Phosphorus is the limiting nutrient, not nitrogen. But yes, it's nearly all from ag and wastewater.

In the ocean, iron plays the role of phosphorus.

And it looks like the evidence for run off causing algal blooms in the Great Lakes is pretty convincing.

I swam in Lake Ontario near Kingston from the mid-80's up to a few years ago and never had an issue, although after heavy rains in summer there could be pretty high E. coli load near shore due mostly to ducks and geese (solution, swim off a dock).

Fecal matter from birds--like the scads of corrmorants around Kingston--is rich in nutrients, and while agricultural runnoff can be a problem Lake Ontario doesn't suffer from it particularly, and even without it there are plenty of altnernative nutrient sources.

I have a photobook of Chicago that has a picture of north avenue beach in the 1960s with thousands of people on it.

I think a city's relationship with its waterfront has to do with what was built on land next to the water. In Toronto the lakefront was industrial until recently. In Chicago the industry was clustered along the river and the lakefront has consisted of parks and beaches for a century.

And now some of our beaches have Blue Flag certification. Incredible.

No one ever even thought about it.

This sounds made up, but my father worked for the state department that oversaw municipal water treatment (as a civil engineer, many cities on Lake Michigan draw water from the lake), so I guess I would have had some awareness of serious issues with the water.

Zebra mussels have had a noticeable effect on water clarity in Chicago harbors in the last ten years. When the light is right it's possible to see 20-30 feet down easily when the view was always previously occluded.

Aside from the detrimental effects on local species it also means that algae and weed blooms are common and it's not uncommon for harbors to be choked with weeds by August.

Not sure if all the current water clarity across the lake can be attributed to them but the change inshore has been rapid and remarkable.

You swam in Lake Michigan regularly? I remember it being bracingly COLD, even on a hot summer day.

This was on the western (Wisconsin) shore of the lake, though, which may have been colder due to upwelling from the prevailing westerly winds.