It took me a little while to get these posted as I tried to determine if they were trumpeter or tundra swans. I'd always assumed that the trumpeters were more common. I found this page, Endangered Resources Program Species Information, at the DNR site and was more confused when I found the EEK! Critter Corner site with information for kids on trumpeter "lookalikes". They have a separate page for Tundras.
Kay mentioned that we only see them in the spring and fall so that means they could be tundra swans. However, she also mentioned that there are lakes in the area that have swans all summer so they could be trumpeters just moving from another area lake.
I've posted a picture below that I took in the spring of 2010 that gives a closeup of the head.
Any bird watchers out there??? Please chime in.