The lakes are the largest freshwater system on Earth, besides what's tucked away in the polar ice caps, and, as this year's extreme drought reminds us, fresh water is a huge resource.
Keeping it clean and plentiful is on the minds of many.
To get a sense of the issues that face the Great Lakes right now, ideastream's Anne Glausser went for a boat ride.
(Lapping sounds of Erie at Wildwood Marina)
Scott Winkler is a biologist with the Ohio Environmental Protection Agency, and I joined him on a recent trip from the Wildwood Marina, just east of downtown Cleveland, out to the middle of Lake Erie.
(Sound of boat engine starting)
WINKLER: We're entering Lake Erie, it's pretty calm today, waves are probably less than a foot and winds are fairly light. It's a very good day to sample.
Winkler takes water samples to measure nutrients and chemicals and creatures, like mayflies and zooplankton and of course, the harmful blue-green algae.
The algae is one of the biggest issues for the lake, says Winkler, along with the threat of Asian carp, an invasive species that has many worried it'll get into the lakes and wreck food-webs and ecosystems. Officials haven't sighted the carp in Lake Erie at this point but have been surprised recently by DNA evidence of them in Sandusky Bay.
These two problems will be front and center during this week's summit on the Great Lakes.
But there are other issues as well.
Erie is a special concern because it's one of the most urbanized of the Great Lakes, and Winkler says, that creates a lot of runoff, including raw sewage.
WINKLER: We have combined sewer overflows, so during times of heavy rains, it will enter the lake.
The bacteria and pathogens in the waste pose health risks to swimmers.
A recent report from the National Resources Defense Council ranked Ohio's beaches as the second most polluted in the country. Euclid Beach was named one of the top 20 most polluted beaches in the nation; it exceeded the Environmental Protection Agency's maximum bacteria standards every year since 2007.
Mercury, PCBs and other toxics are another concern. These chemicals build up in fish and when people eat the fish, it can cause health problems, such as issues with learning and memory. There are fish consumption advisories for all of the great lakes.
WINKLER: The mercury is mainly from the coal burning plants and it's in the atmosphere and it's in the environment.
It's in rain and snow.
Once we get to the sampling location, Winkler points out smokestacks in the distance:
GLAUSSER: And so that's what's putting out some of this mercury that ends up in Lake Erie. WINKLER: Well, it's carried by the wind, so it's mainly plants to the west--our prevailing wind is southwest--so Chicago, things out in Illinois, Indiana, is coming this way and if we would be putting anything into the air, it's moving further east, normally. GLAUSSER: So what other states do affects us. WINKLER: Absolutely.
Winkler starts his sampling.
WINKLER: Those little green balls--that is probably microcystis.
That's the harmful algae. It's not too bad this year because of the summer drought.
Winkler has been keeping an eye on Erie since 2010, and he says it's a dynamic lake where conditions change quickly.
It's an important fishery.
WINKLER: Lake Erie is a huge recreational interest, and because it's the shallowest and the southern-most and the warmest and the most nutrient rich, we have far more fish than any of the other great lakes.
So keeping the fish healthy is a major goal. Winkler mentions a recent fish kill in an area to the east of us, through Lake County. They think the spot was a dead zone, meaning there was no oxygen so the fish died.
This is the kind of event researchers like Winkler are trying to understand and do something about.
And it makes sense to keep close tabs on Erie. As one Kent State biologist put it, Erie is a bellwether lake, a canary in the coal mine.
And those attending this week's conference aim to keep that bird alive.