Gary,
Welcome to the board. After reading your questions and comments from others, it seems to me that you have enough information to do some research on the topic....specifically regarding damage to rivers and lakes created by engine usage. Another point (made by Stacie) was that some regulations are in place primarily to limit use by people with power toys, which I must say I am all in favor of since a certain percentage of the population does not excercise good judgement and/or discretion in this regard. If you come across some good information on the topic please share it with us.
JMS