Ohio's Revised Code is available on-line. I go to the Ohio Highway Patrol web page and hit the link.
You will find ORC 2923.12 to .16-ish handles a goodly portion of gun laws. The only thing that is specifically banned by state law is concealed carry (prudent person rule aside) and loaded vehicle carry (must be either in locked case, or in plain view, action open, and unloaded). There are two recent Ohio court cases that say that in the second example the ammunition may be kept on your person (in mags or speedloaders) however not all of the LEOs I called were aware of this. The Ohio Atty General has an LEO training video on this very subject which you can ask to see (OHP posts have this video) but they may not let you (officer safety, no doubt).
There is no state law that bans open, loaded carry of a firearm. But Ohio has no state preemption which means that your county, city, or township could conceivably have some sort of ban.
You task is to do the research, call all the agencies, and inform them of the law, if they do not already know it. Call your sheriff and local PD, and constable and OHP post and tell them that you intend to carry openly while fishing and would appreciate that they do not infringe on your right to self defense. Probably not a problem in rural counties...I can't vouch for Cleveland
Also, you should use TFL's excellent search engine to see if your topic has already been discussed, as this one has many times.
In fact, it would be better if you had already done the research and reported back to us. That way we all have the chance to learn something new rather than re-hashing the same old stuff.
Rick
Phx, Az