The latest data I have been able to find (utilizing a variety of studies) show that in 2003 all registered boats in the US (including the States, commonwealths & territories) totalled just under 13 million...an
increase of over 55% in the twenty year period studied. Additionally, as mentioned by ApS, there are an estimated 8 million additional watercraft (rowboats, kayaks, canoes, small sailboats, etc.)in the US alone that do not need to be registered in the State they are used.
The same studies all consistently show that as the number of recreational watercraft continue to swell, overall safety on the water also continues to improve.
Anyway, I can think of no waterway that I have boated on in the last 40 years that has seen a decrease in boating population.
Merry Christmas,
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