Suppose one lives next to a lake or a pond and has a canoe (or a kayak or other non-motorized, sail-less rowboat) that is kept docked at the water. May one use it on Yom Tov? Is this melacha? Does it count as "traveling" if one has no destination and is simply paddling around and returning to his point of departure? What if one is not paddling but simply riding along? Would the answers be different on Shabbat?
The Shulchan Aruch 339:7 implies that one is only allowed to enter a docked boat if he is not moving it around:
סְפִינָה, אִם הִיא יוֹשֶׁבֶת בְּקַרְקַע הַיָּם וְאֵינָהּ שָׁטָה כְּלָל, מֻתָּר לִכָּנֵס בָּהּ; וְאִם הִיא קְשׁוּרָה כְּמִנְהַג הַסְפִינוֹת הָעוֹמְדוֹת בַּנָּמֵל, אַף עַל פִּי שֶׁהִיא שָׁטָה עַל פְּנֵי הַמַּיִם, מֻתָּר לִכָּנֵס בָּהּ.
One is allowed to enter a boat if it is resting on the ground (bed) of the sea and is not floating at all. If it is tied as is customary with boats docked in a port, even though it is floating on the water, one is allowed to enter it.
As far as riding along even when e.g. a non-Jew will be sailing the boat, this is a potential problem even when one boarded before Shabbat if one would still be on board on Shabbat (see Shabbat 19a cited here).
(These laws are true for both Shabbat and Yom Tov. As noted by @DoubleAA, there may also be an issue of techum shabbat, if one were to travel more than ~3100 feet, since a lake generally doesn't have residences on the water. Also, with regard to Yom Kippur, there is an additional issue of getting wet in a way which might be considered taanug.)
One may do so, provided it's tied to something on the shore. [Obviously, he won't get very far.] Shulchan Aruch 339:7. However, see the commentaries there for details and exceptions. And, if this is a practical question for you, ask your rabbi rather than relying on what you read on this site.
Note that there's no explicit prohibition on "traveling", though various methods of travel are prohibited for various reasons. Boarding and traveling by a boat is (with an exception outlined above) among them.