Yes the great blue heron does have many predators.
Some of the predators of the great blue heron are raccoons, eagles and hawks.
The raccoons, eagles and hawks will prey on adult great blue herons.
Some other animals that will prey on the great blue heron eggs are crows and raccoons but the other predators including the raccoons prey on the adult great blue heron.
Great blue herons are pretty well protected by law and it's illegal for humans to kill great blue herons unless they have a very good reason to do so.
The fine for killing a great blue heron can vary depending on the laws in your location and whether or not you have any prior criminal history or if it's your first offense at killing the great blue heron or if you've killed more than one and it's been your second or third offense.
If it's your first offense and you killed a great blue heron without any permit then you'll likely get a $700.00 fine but it might even be up to $4,000.00 depending on the local laws.
If it's your second offense or you have other criminal history then the fine for killing a great blue heron can be as much as $15,000.00 and 6 months to a year in prison.
Some places will be very strict with the law about killing a great blue heron and may actually go ahead and fine you the $15,000.00 and then even impose a prison sentence of between 6 months to a year.
So do not kill a great blue heron unless absolutely necessary.