A friend of mine has a SeaRey amphib. It is a slow flying boat. We take it to the lake sometime, fly around, not too low, not buzzing any boats. Usually we get thumbs up from boaters and jetskiers, we haven't pi**ed anyone off so far. (or haven't seen anyone shake a cane at us)
Unless they have video of you buzzing someone intentionally in a SeaRey, you can break the 500' rule in an amphibious plane according to the rules. The very first line says "except when necessary for takeoff or landing". The lake is your runway in that plane. My interpretation may be different than the FAAs. If I got a call after flying that plane, my intention was to land and that's why I was so slow. After looking around, I decided the lake was too crowded and I went around!
Or you could buy a trike or powered parachute and then it just says they may be operated at less than the minimums.
§ 91.119 Minimum safe altitudes: General.
Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:
(a) Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.
(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.
(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.
(d) Helicopters, powered parachutes, and weight-shift-control aircraft. If the operation is conducted without hazard to persons or property on the surface -
(1) A helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section, provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA; and
(2) A powered parachute or weight-shift-control aircraft may be operated at less than the minimums prescribed in
paragraph (c) of this section.