NATVA
NATVA (National All-Terrain Vehicle Association) was the official amphibious races and had a magazine "Races started around 1969, but I don't know when they finally ended. Most of the races were in the northeast and upper midwest. I have a NATVA magazine that shows regions covering the whole country, but as far as I can remember they never had a race schedule for all of them. Michigan, Wisconsin, Ohio, Indiana, Pennsylvania, New York, New Jersey, Maryland, and Virginia are the states I know for sure, but there are probably more.
There were four "National" events a year and regionals most every other weekend or so someplace in the country. Most of the teams that did really well owned dealerships or part of an ATV manufacturing company. They had the advantage of cheaper parts and direct tech knowledge from the source. In 1972 and 73 Scott Slonaker was probably the most dominant, then Larry Shorts, Larry Smith, the McKays (all Attex) and the Fischer Scrambler team out of Ashtabula Ohio. There were an awful lot of competitive Max drivers, but the ones I remember were individuals and not part of a race team. I'm sure there are more that I'm forgetting, and others that took over in later years". The NATVA races were quite the events to attend, attracting thousands of spectators.
Read more about this topic: Amphibious ATV