Protect the lakes from the sorts of abuses they suffered on a massive scale prior to modern environmental regulations were enforced, and from additional threats like microplastics, fertilizer run-off, sewage, contamination from watercraft, future outbreaks of invasive species transported by ocean-going shipping vessels, large-scale diversion for irrigation or urban water consumption, and a host of other things.

The way you asked it was like "What problems?" when it's obvious that a water-system that vast needs controls or it'll be abused and ruined for everyone.