I got a call the other day from a Marine Division Sheriff that was concerned because there was almost a fist fight between a boater and a diver. He was asking if it was one of my divers. Since it wasn't I didn't give it much thought until now.
I agree with Paula about the boaters not knowing what a dive flag is, but I have to jump on the side of boaters when you are diving in a Marina, channel, river or in this case off a boat ramp. The true definition of the dive flag law is that it is a courtesy and if my interpretation is right, only applies if the dive flag is attached to a boat or vessel at least 36 inches above the water. The true dive flag (international blue and white alpha flag) and the recreational dive flag means "divers below stay clear at idle speed" It is legal for a boat to approach a dive flag if they are doing so with a lookout and they have reduced their speed to "the bare minimum necessary for safe navigation." The flag is necessary for another boat to avoid a collision with the parked dive boat, not to keep the divers safe.
The rules of the road are different if you are diving in a restricted waterway... you become the burdened party. If it is not possible for a boat to maneuver to avoid you or your flag due to restrictions in navigation such as, "I have to take my boat out at that ramp," "the canal is less than 100feet wide," or "that is the only path through the body of water that can be safely navigated," then you are really not supposed to be diving there. If you decide to dive there then it is YOUR responsibility to stay clear, not the vessel that is restricted.
I know there can be a lot of arguments but to give you a super simple example, if you were diving in a shipping channel with a flag, would you expect the flag to stop a freighter? Same rules apply. If a freighter was traveling to the boat ramp, it would not be expected to stop but it would be expected to reduce speed. It could run your flag bodily down if it was doing so in a restricted waterway at bare steerageway to avoid damage to the vessel. Another illustration would be the pedestrian trying to cross a freeway. While it illegal for a car to hit that pedestrian, the pedestrian should find another way.
In the case of the boat ramp operator, his decision to keep you out is probably his only solution.
I tend to avoid boat access points and ramps in the summer. I dive the river in the winter mostly.
Safe diving,
Rich