That restriction was for State owned fish and wildlife areas only. People could still fish on privately owned lakes.
www2.illinois.gov
I remembered that because when they opened back up it was something like two people from the same family could enter state fish areas to fish but had to maintain some large distance between themselves an others. My thought at the time was that preventing two people from the same family from fishing on the side of a state owned fishing area had an almost zero chance of spreading the virus to begin with. My thought at the time was that even if an immediate shutdown was necessary, that things that are very low risk should have been looked for and relaxed within a few days or weeks. In Michigan, they set up a regulation that didn't allow people to visit a vacation home if both homes were in Michigan. You could move between a house in Michigan and a house in another state, but if you owned a home and a vacation home both inside Michigan, you could not travel between them. I never heard of anyone being cited for violating that regulation, but simply having that regulation makes no sense. Having non-sensical restrictions doesn't prevent spread of disease and erodes public trust of the government.
@SnidelyWhiplash has stated that people conforming to safe practices is the important thing. Political battles between governors imposing apparently nonsensical government restrictions and governors apparently deriding safe practices didn't help. I would say that neither of those positions helps get the public to follow safe practices.