What if there was a lake on the Moon? What would it be like to swim in it? Presuming that it is sheltered in a regular atmosphere, in some giant dome or something. -- Kim Holder

This would be so cool.

In fact, I honestly think it's cool enough that it gives us a pretty good reason to go to the Moon in the first place. At the very least, it's better than the one Kennedy gave.

Floating would feel about the same on the Moon as on Earth, since how high in the water you float depends only on your body's density compared to the water's, not the strength of gravity.

Swimming underwater would also feel pretty similar. The inertia of the water is the main source of drag when swimming, and inertia is a property of matter[1] independent of gravity. The top speed of a submerged swimmer would be about the same on the Moon as here—about 2 meters/second.

Everything else would be different and way cooler. The waves would be bigger, the splash fights more intense, and swimmers would be able to jump out of the water like dolphins. //

but the bottom line is that a normal swimmer on the Moon could probably launch themselves a full meter out of the water, and Michael Phelps may well be able to manage 2 or 3. //

But it gets even better. A 2012 paper in PLoS ONE, titled Humans Running in Place on Water at Simulated Reduced Gravity, concluded that while humans can't run on the surface of water on Earth,[5] they might just barely be able to do so on the Moon. (I highly recommend reading their paper, if only for the hilarious experimental setup illustration on page 2.)