You don't have to have the ability to walk on water to get to Spirit Island by foot from the mainland. You could just simply walk there. But you probably don't want to do that or you would make a whole bunch of tourists angry for ruining their pictures of one of the most photographed spots in the Canadian Rockies.
You can only get to Spirit Island by taking the Maligne Lake boat tour (well, you could probably hike there but it might take a while). The boat tour was a little pricey but I guess the beautiful scenery we saw during the tour made it worth it.
We had to sit around waiting for our boat for quite a while. I remember us making some stupid videos while waiting because we were bored. There wasn't really much to do there otherwise. Well, we could've rented a canoe or a kayak, but that would've been redundant. At least the surrounding view was pretty.
Spirit Island is located on Maligne Lake within Jasper National Park, which is one of my favourite Canadian national parks. If you have to choose between Jasper and Banff National Parks to visit, go for Jasper. You won't regret it! It's just as beautiful but not as touristy. Too bad it's about four hours away from where we will be in June.