Make certain it is not a Corps of Engineers lake. They have their own rules about firearms. If it is a Corps lake check with your local Corps office. I did.
Thank you for your inquiry.
The answers to your questions can be located by reading CFR Title 36 - Parks, Forests and Public Property, CHAPTER 111 - U.S. ARMY CORPS OF ENGINEERS, Part 327 - Rules and Regulations Governing Public Use of Water Resources Development Projects Administered by the Chief of Engineers.
(a) The possession of loaded firearms, ammunition, loaded projectile firing devices, bows and arrows, crossbows or other weapons is prohibited unless:
(1) In the possession of a Federal, State or local law enforcement officer;
(2) Being used for hunting or fishing as permitted under 327.8, with devices being unloaded when transported to, from or between hunting and fishing sites;
(3) Being used at authorized shooting ranges; or (There are no authorized shooting ranges on USACE property at Lavon Lake.)
(4) Written permission has been received from the District Commander.
Would it be permissible for someone to take a handgun on a boat on Corps property holstered without magazine inserted?
No. Section 327.13 (a) (1) clearly states the possession of loaded firearms or ammunition is prohibited.
Is the water on the lake considered corps property or is the Corps property only the parking and launching facilities?
The rules and regulations stated in Title 36 CFR shall be applicable to water resources development projects, completed or under construction, administered by the Chief of Engineers. The term "project" or "water development project" refers to the water areas of any water resources development project, to all lands owned in fee by the Federal Government and to all facilities therein or thereon of any such water resources development project.
Under what conditions is carrying a handgun on Corps property allowed?
Possession of a loaded handgun (concealed or not) by a member of the public is a violation of Title 36 CFR Section 327.13.
If you have additional questions or if you would like to speak with me directly, please feel free to call.
Nonsense, I have not yet begun to defile myself.