(AREA) -- Scientists and policymakers are discussing issues related to Great Lakes water levels during a conference in Ann Arbor. The event hosted by the Environmental Law and Policy Center began Wednesday and concludes Thursday. Among interest groups represented are shipping, water utilities, industry and advocates for the environment and homeowners. Water levels have been a contentious matter for decades. They were so high during the 1980s that cottages were washed into Lake Michigan. But they've been unusually low since the late 1990s. Heavy snow and rain have boosted levels this year, although Lakes Michigan and Huron remain below normal. Some advocates want to restore their levels by placing structures in the St. Clair River that would limit outflow from Lake Huron. Opponents say doing so might cause flooding in some places.