Arthur Lake is actually pretty obvious if you are big into Arthurian Legend. Arthur, obviously, relates to King Arthur, while there are a couple of possibilities for Lake. Most likely in my mind is that Arthur is tied very closely to a lake, and specifically a lake spirit. She is the one who gives him Excalibur (the sword that was in the stone was a different sword that is either broken or lost during his early adventures) and he must return the sword to her once he is done with it (usually done by Galahad after his death). The other possibility is a link to Lancelot, as Lancelot's actual sirname was du Lac, or "from the lake".
Link to the book:
Captain Courageous Comics 6