The changes caused by declining ice cover on the Great Lakes are pretty bad, but it's not all doom and gloom. Ice cover on the Great Lakes has declined in the past 40 years with average ice coverage dropping up to 75 per cent, depending on the lake. "We rely a lot on the Great Lakes for shipping ... so an ice-free Great Lake is not a barrier to shipping. But beyond that there are a lot of negatives associated," said Mike McKay, the executive director for the Great Lakes Institute for Environmental Research (GLIER), based at the University of Windsor.