Why did the lake start a band? Because it had a lot of good “current” flow!

And that’s why this pun is fun: This pun is fun because it plays on the double meaning of “current”—both the flow of water in a lake and the flow of electric current in a band (music). To get the humor, you need to know that lakes have currents, and bands have a musical flow or energy. It’s a playful mix of nature and music terms.