Last I checked, you're required to always use a dive flag -- for good reason -- and must stay within 75 ft of it. Wouldn't want to wreck my prop by hitting you!
Also, if you are blocking a channel by diving there, common sense would tell most people that a) it's dangerous, b) it's inconsiderate and c) it might be a violation of state laws/regs. So they wouldn't do it -- duh! If you need an MP to explain that to you, you may be breathing something other than just compressed air! If you do it again after being told by an MP that it's not permitted, you deserve a ticket and good luck with your court case!
I've also found in 20+ years on the lake that the MPs do a pretty good job. They've come promptly when I've called them and performed their duties courteously and professionally. Pretty thankless job, really.