Waterways across the upper Midwest are increasingly plagued with ugly, smelly blue-green algae that's killed dozens of dogs and sickened people.

The algae is blooming in response to drought and fertilizer runoffs from farm fields.

Aquatic biologists say it's a problem that now falls somewhere between a human health concern and a nuisance, but eventually it will lead to more human poisoning.

While no one has died from the algae's toxins yet, many have been sickened.

Experts say at least six lakes in western Wisconsin have been hit particularly hard. Blue-green algae is the No. 1 water quality issue in Oregon.

The scum also has killed dozens of dogs -- including at least four in Oregon, three in Wisconsin and one in Minnesota this summer.