Organizers announced earlier this week that representatives of Romney and President Barack Obama would outline the candidates' positions Thursday on matters affecting the lakes at the forum in Cleveland.
The event is part of the annual Great Lakes Restoration Conference. More than 600 environmental activists, government officials and scientists are registered.
Former Obama energy and climate advisor Carol Browner is scheduled to speak on the president's behalf.
Advocates have asked both campaigns to pledge further support of a federal initiative that has supported hundreds of Great Lakes restoration projects.
They also want barriers placed in Chicago waterways keep Asian carp out of the lakes.